Who among the living knows that Ned declared for Stannis?

[Thucydides]

The people remaining in the story who are definitely or possibly in the know are as follows (best I can tell -- please post corrections, clarifications, and additions in the comments, and I'll make the corrections here):

Named living people who definitely know

• Varys: 1st hand witness
• Lord Petyr Baelish: 1st hand witness
• Queen Dowager Cersei Lannister Baratheon: 1st hand witness
• Sandor Clegane (assuming he is the gravedigger on the Quite Isle): 1st hand witness
• Ser Barristan Selmy: 1st hand witness
• Ser Boros Blount: 1st hand witness
• Ser Maryn Trant: 1st hand witness
• Sansa Stark: Cersei shows Sansa the letter that Ned wrote to Stannis, which Cersei intercepted; does not know Petyr Baelish's role
• Harys Swyft: Hand to the King on Cersei's "Smallest Council" when Cersei says Lord Eddard Stark "would have handed the realm to Stannis" (AFfC p292); may not know Petyr Baelish's role
• Lord Orton Merryweather: Master of Laws on Cersei's "Smallest Council" when Cersei says Lord Eddard Stark "would have handed the realm to Stannis" (AFfC p292); may not know Petyr Baelish's role
• Aurane Waters: Master of Ships on Cersei's "Smallest Council" when Cersei says Lord Eddard Stark "would have handed the realm to Stannis" (AFfC p292); may not know Petyr Baelish's role
• Qybrun: Master of Whisperers on Cersei's "Smallest Council" when Cersei says Lord Eddard Stark "would have handed the realm to Stannis" (AFfC p292); may not know Petyr Baelish's role

Unnamed living people who definitely know

• The royal steward (assuming he hasn't died): 1st hand witness
• Surviving Lannister guards (number unknown): 1st hand witnesses
• Surviving members of the City Watch of King's Landing (Gold Cloaks; number unknown): 1st hand witnesses

Other living people who may know what happened

• Princess Myrcella Baratheon: 1st hand witness (may not remember)
• Prince Tommen Baratheon: 1st hand witness (may not remember)
• Ser Jaime Lannister: likely told by Cersei
• Tyrion Lannister: may have been told by Tywin or Cersei
• Illyrio Mopatis: may have been told by Varys
• Bloodraven: may have seen it using powers
• Bran: may have seen it using powers
• Ser Alliser Thorne: may have been told by the late Janos Slynt, who was a 1st hand witness

Why this information may be important

The exact circumstances of Ned's arrest could provide two pieces of information that would be very valuable if they were divulged at the right moment to the right people. Specifically, the fact that Ned died defending Stannis's right to the throne, and the fact that Petyr Baelish betrayed Ned.

Ned's statement at the Great Sept of Baelor is "I plotted to depose and murder his son and seize the throne for myself" (AGoT p701) -- The confession that the Lannisters force upon Ned pretends that Ned never declared for Stannis.

The Lannisters likely know that this is valuable information at the time that Ned dies, and it obviously serves their interests to withhold it from public consumption. It is not obvious that Cersei considers this information important any longer, given the offhand way that she refers to Ned's declaration when speaking to her "Smallest Council." Perhaps her belief that Stannis is doomed has caused her to let down her guard.

Would Stannis be better disposed toward the Starks if he learned that Ned had died to back his claim? Would the North be more sympathetic to Stannis if they knew that?

When I was reading the scene in AGoT where the Northern Lords discuss whose claim they should support, and Robb keeps gravitating toward Stannis while some insist that Renly has already been crowned, I was shouting at them in my head, "It's Stannis! Ned died declaring for Stannis!" And then, it's all over because the Greatjon foolishly declares for Robb as King of the North. Surely if they'd have known that Ned died backing Stannis, they'd have backed him. I have a similar reaction every time Stannis speaks begrudgingly of Ned. There's irony in the fact that Stannis is utterly unaware that Ned died declaring for him.

Having said all this, it's worth noting that in the show, Stannis does receive the letter that Ned wrote, which never reached Stannis in the book (Cersei shows the intercepted letter to Sansa on p528 of AGoT). To be sure, the show is not canon, but this may point to GRRM's plan to ignore Ned's declaration in the story. Or not. The show could make up for it in another way. (One could very well wonder what happened to this letter, and whether it will resurface.)

Even so, let's speculate on who might divulge this information about Ned's declaration and why. Since the information is damaging to the claim of the enthroned Lannister bastards and to Petyr Baelish's pretense that he is Sansa's protector, there seem to be three key reasons for a character to divulge this information: It may assist the Starks in reaching a reconciliation between Stannis and the North, and it could expose Petyr Baelish's treacherous role.

Survey of possible outcomes

Sandor may well offer the information to someone at a key moment as part of his redemptive story arc. He might confess his role in Ned's betrayal. He may outright use the information to help the Starks reach a reconciliation with Stannis and the North (see the recent thread "Is the Hound a fan of the Starks?"; I'm inclined to think that the Hound is well disposed toward them, though I'm skeptical that he lives on as the Gravedigger.) Or Sandor may have an opportunity to use the information to inform Sansa about Petyr Baelish and save her from him. Sansa already knows that her father declared for Stannis, but does not know of Petyr Baelish's treachery.

Varys, Illyrio, and Petyr have separate agendas and could use this information at any time, though I view it as unlikely that Varys or Illyrio will put this information to any good use, because at this point in the story they want to maximize polarization in Westeros. Petyr may use it to manipulate a situation somehow, leaving out his own crucial role.

Tyrion and Barristan have become outright opponents of the Lannisters. It's difficult to see a situation in which Barristan would divulge this information to anyone to whom it mattered. Maybe to Dany, but to her it will just be another story about the Userper's dogs. It's also difficult to see how Tyrion would use the information, though he may do it just to oppose Cersei's interest and combine two of her opponents (viz., Stannis and a Bolton-free North). Nevertheless, Tyrion may have a credibility problem.

Jaime still has some loyalty to his house and family. However, with his newfound view of honor, his notion that "A Lannister always pays his debts," and his penchant for telling Starks gruesome stories about how their loved ones died at the hands of kings, Jaime may very well spill the beans. Perhaps he does this to the BwB, because this may be a piece of information that he could use to bargain for his life. This could result is a widespread dissemination of accurate information, though such rumors may not be considered reliable enough to influence lords in matters of war and peace.

Alliser may tell someone in the Night's Watch so that the word gets to either Stannis or Jon (assuming Jon's part in ASoIaF continues), but it's unlikely that he'd tell either of them directly. Alliser would not seem to want Jon to know that Ned declared for Stannis, because Jon would consider Ned's declaration for Stannis as exculpatory evidence that would explain Ned's actions and why the Lannisters arrested him.

Bran or Bloodraven may communicate this information to Stannis

Perhaps when Stannis takes Theon to be executed by the Weirwood, per Theon gift chapter.

The members of Cersei's "Smallest Council" have scattered all over the world, with the exception of Qyburn, who remains in Kings Landing (though he no long sits on the Small Council). Orton Merryweather returned to Longtable in the Reach. Aurane Waters absconded with the crown's navy in the confusion following Cersei's arrest. Harys Swyft is in Braavos to deal with the Iron Bank in person. It's not at all clear whether their knowledge will prove to have direct significance, but the fact that Cersei leaked the information of Ned's declaration for Stannis indicates that the spread of this knowledge is not unprecedented.

The rest of the surviving Kingsguard, Lannister guards, and Gold Cloaks are non-entities. Some may be honor-bound not to talk about it. Those who do talk about it (e.g., in pubs and brothels in King Landing) will have their story drowned out by the noise of false rumors. Unless one of them reappears, Wex-like, to divulge the secrets directly to a leader of the opposition, the will not be considered reliable enough to influence lords in matters of war and peace. It is highly unlikely that this group, which hasn't been heard from in four books, will suddenly surface again to have a major impact on the story.

I doubt that Tommen or Myrcella could coherently explain what happened even if they wanted to.

My guesses

I am inclined to think that Ned's declaration will come to light at some point. However, there seems to be no textual evidence to suggest how or when.

So if I had to guess, I'd say that Sansa runs into Sandor as the Gravedigger. She is accompanied by Petyr Baelish and disguised at Alayne Stone. Sandor recognizes her and surmises from her disguise and her companion that she's under his control. Sandor tells Sansa of Petyr Baelish's part in her father's death, which she can trust to be true because it aligns with the details she saw in her father's letter to Stannis.

As a runner up, I'd say that Jaime bargains for his life with the BwB using this peace of hitherto undisclosed information about Ned's declaration and Petyr's treachery, leading Lady Stoneheart to add Petyr Baelish to the top of her shit-list alongside Walder Frey. This may put Sansa in a compromising position, since she's been acting as Petyr's collaborator, and it's notoriously difficult to escape guilt-by-association with Lady Stoneheart (e.g., Brienne's experience).

As a runner up to that, I think that Ned's letter to Stannis may surface, get obtained by someone friendly to Stannis, who can then use it as a device to get buy-in from the post-Bolton North.

Since these are just guesses, I'm interested in hearing people theorize about it and discuss it in order to refine my own thoughts and find out what I've missed.

Changes
ETA: corrected mistaken reference to Sandor using his brother's name Gregor per comment from Minstral.
ETA: Bloodraven and Bran to the possibles list per comment by Arya kiddin', along with suggestion of how they may use the information.
ETA: citation for Cersie showing Ned's intercepted letter to Sansa per TheStarkInWinterhell's comment
ETA: clarification about Ned's confession
ETA: Sansa contenrt
ETA: Alliser Thorne content per TheCrannogDweller's comment
ETA: Members of Cersei's Smallest Council per MRHD

[Aetta]

This bugged me, that Stannis is kind of a jerk about Ned when he is talking to Jon about him, indicating Ned was no special friend to him. I was thinking same as you, where's the love, man?.

However, I chalked this up to Stannis' personality. To me, Stannis wouldn't have seen Ned as doing him any favors, rather he would think it was Ned's DUTY to declare for him if he knew what Jon Arryn knew. He's just not a "Thank You" kind of guy.

[GallowsKnight]

Wasn't it part of the treason charge against Ned? Publicly announced outside the sept of baelor.

[King Pellinore]

Robert liked Ned better and then Ned had the gall to be honorable towards Stannis every time their paths crossed.

"People find it far easier to forgive others for being wrong than being right.
Albus Dumbledore"

[Rysler]

I think they claimed Ned was trying to take the throne for himself. The Lannisters didn't want the people of KL to question Joffrey's claim.

[Ahura Mazda]

I am sorry, I might be confused with the TV show, but didn't Ned Stark send for a message to Stannis Baratheon pretty much saying that he wanted to place him as King? Did it ever reach its destination? I thought it was mentioned by Davos in one of his first chapters.. it has been a long time since I read it, I am probably wrong.

[Minstral]

Wasn't it part of the treason charge against Ned? Publicly announced outside the sept of baelor.

That is the one where he "confesses" to trying to usurp the crown for himself.

BTW Thucydides, you said Gregor again.

[Minstral]

I am sorry, I might be confused with the TV show, but didn't Ned Stark send for a message to Stannis Baratheon pretty much saying that he wanted to place him as King? Did it ever reach its destination? I thought it was mentioned by Davos in one of his first chapters.. it has been a long time since I read it, I am probably wrong.

He did not in the books. Stannis already investigated with Jon Arryn.

Edit: He sent the letter yes, but it never reached Stannis.

[King Pellinore]

Cersei showed the blood stained letter to Sansa.

[Arya kiddin']

Bloodraven knows everything. Don't count Bran out either.

[Thucydides]

BTW Thucydides, you said Gregor again.

Thanks for pointing that out. Fixed.

[Thucydides]

Bloodraven knows everything. Don't count Bran out either.

Good point. Added them to the possibles list, plus a brief commentary on what they would do with the information.

[TheStarkInWinterhell]

"The queen picked up a letter. The paper was torn and stiff with dried blood, but the broken seal was her father's, the direwolf stamped in pale wax. "We found this on the captain of your household guard, Sansa. It is a letter to my late husband's brother Stannis, inviting him to take the crown."

[Thucydides]

"The queen picked up a letter. The paper was torn and stiff with dried blood, but the broken seal was her father's, the direwolf stamped in pale wax. "We found this on the captain of your household guard, Sansa. It is a letter to my late husband's brother Stannis, inviting him to take the crown."

Thanks for quoting that. The show diverges from this, as I point out in my second paragraph, and that may have confused people about the books. This should clear up any misunderstanding.

I've added a citation to that passage to the main post. Plus, I've added Sansa to the 2nd-hand witness list.

[Thucydides]

Wasn't it part of the treason charge against Ned? Publicly announced outside the sept of baelor.

Eddard's "confession" consists of him saying that he tried to take the throne for himself, not for Stannis.

Here is Lord Eddard Stark's confession in front of the Great Sept of Baelor (note the bolded text):

When the bell ceased to toll, a quiet slowly settled across the great plaza, and her father lifted his head and began to speak, his voice so thin and weak she could scarcely make him out. People behind her began to shout out, "What?" and "Louder!" The man in the black-and-gold armor stepped up behind Father and prodded him sharply. You leave him alone! Arya wanted to shout, but she knew no one would listen. She chewed her lip.

Her father raised his voice and began again. "I am Eddard Stark, Lord of Winterfell and Hand of the King," he said more loudly, his voice carrying across the plaza, "and I come before you to confess my treason in the sight of gods and men."

"NO," Arya whimpered. Below her, the crowd began to scream and shout. Taunts and obscenities filled the air. Sansa had hidden her face in her hands.

Her father raised his voice still higher, straining to be heard. "I betrayed the faith of my king and the trust of my friend, Robert," he shouted. "I swore to defend and protect his children, yet before his blood was cold, I plotted to depose and murder his son and seize the throne for myself. Let the High Septon and Baelor the Beloved and the Seven bear witness to the truth of what I say: Joffrey Baratheon is the one true heir to the Iron Throne, and by the grace of all the gods, Lord of the Seven Kingdoms and Protector of the Realm."

[bold emphasis added]

I've added a short paragraph to clarify this in the original post.

[TheCrannogDweller]

Here is Lord Eddard Stark's confession in front of the Great Sept of Baelor (note the bolded text):

I've added a short paragraph to clarify this in the original post.

Hah. Notice how he doesn't mention the Old Gods when he confesses his treason.

Btw, Janos Slynt was also present, so he should be on your list.

I haven't been able to find textual proof yet, but there is a chance that through him, Alliser Thorne and Jon Snow might also be aware of Ned's intentions.

[Thucydides]

Btw, Janos Slynt was also present, so he should be on your list.

I haven't been able to find textual proof yet, but there is a chance that through him, Alliser Thorne and Jon Snow might also be aware of Ned's intentions.

Janos Slynt is dead. I'll add Alliser to the possible list. Janos may have rubbed Jon's face in the fact that he betrayed Ned, but I don't think he would have told Jon the real reason Ned was arrested, because Jon would consider that exculpatory evidence against Ned's treason.

[Stan the Man Baratheon]

My question to OP is, how do you think will it play out, considering you have sampled possibly all factors?

[Thucydides]

My question to OP is, how do you think will it play out, considering you have sampled possibly all factors?

I am inclined to think that Ned's declaration will come to light at some point. I have not found any textual evidence to suggest that it will turn out one way or another.

So if I had to guess, I'd say that Sansa runs into Sandor as the Gravedigger. She is accompanied by Petyr Baelish and disguised at Alayne Stone. Sandor recognizes her and surmises from her disguise and her companion that she's under his control. Sandor tells Sansa of Petyr Baelish's part in her father's death, which she can trust to be true because it aligns with the details she saw in her father's letter to Stannis.

As a runner up, I'd say that Jaime bargains for his life with the BwB using this peace of hitherto undisclosed information about Ned's declaration and Petyr's treachery, leading Lady Stoneheart to add Petyr Baelish to the top of her shit-list alongside Walder Frey. This may put Sansa in a compromising position, since she's been acting as Petyr's collaborator, and it's notoriously difficult to escape guilt-by-association with Lady Stoneheart (e.g., Brienne's experience).

As a runner up to that, I think that the letter to Stannis may surface, get obtained by someone friendly to Stannis, who can then use it as a device to get buy-in from the post-Bolton North.

Since these are just guesses, I'm interested in hearing people theorize about it and discuss it in order to refine my own thoughts and find out what I've missed.

ETA: fixed 2nd reference to Sandor, in which I (once more) called him Gregor.

[Stan the Man Baratheon]

-snip- (you used Gregor instead of Sandor)

I am inclined to believe the contents of the letter will never re-surface. But i like your Grade A scenario.