How old bear became lord commander?

[Prince Yourwetdream Aeryn]

Is it possible that Mormont was chosen because he was too fat? Because from writer's perspective, being fat increases your potential to do great things (like samwell tarly, mace tyrell and wyman manderly).

Who were other candidates? Did Benjen Stark participate in the election?

[1000th Lord Commander]

Looking at the timeline, I'd say Benjen probably did participate in the election. Benjen joined the watch shortly after RR, While Jeor has been in the watch longer than Thorne, who also joined following RR. The last election was 288AC, So both Benjen and Thorne would have voted in it, Robert's Rebellion happening in 283 AC.

The being fat thing is ridiculous, however.

[Adam Yozza]

We don't really get given a time for when Jeor joins the Watch. I always assumed it was at the end of RR, since we don't hear about Jorah doing anything until the Greyjoy Rebellion. I could be wrong though.

Anyway, he was probably chosen because of a variety of factors such as experience in battle; both as a soldier and commander; and the fact that he was a Lord in his own right before being elected.

Benjen Stark was there but I don't think he was in the running in it. Though there are some exceptions, for the most part it's the older/most experienced brothers who participate. But he had been there for five years and was well liked so it's not impossible. I imagine Qhorin Halfhand also competed, along with Jason Mallister and Cotter Pyke.

The being fat thing is stupid, not least because he's not actually fat.

[YOVMO]

16 minutes ago, Adam Yozza said:

and the fact that he was a Lord in his own right before being elected.

This is an important factor....also that he was a Northern Lord.

[The Commentator]

The Old Bear was carrying extra padding but that's not the same as Samwell's bulk make up.  The Old Bear was 68.  That's just the kind of extra fat that older people get.  He's not obese like Sam.  Sam's is baby fat that never went away.  

Mormont was probably a ranger at first before he got elected.  

[Coolbeard the Exile]

I think you are onto something Brandon Baratheon it's probably because he was fat.

[White Ravens]

Benjen probably wanted the job but finally realized that he just wasn't fat enough to compete with the Old Bear. 

[GyantSpyder]

They elected the Old Bear because of his natural ability to commandeer unsecured peanut butter from nearby smallfolk, and to catch salmon.

When they won, though, he had his head stuck in a honey tree. Whole bunch of folks had to pull him out. It was a whole thing.

[The Bastards Giant Friend]

They used to have two great platforms suspended via a pulley at the top of the wall. They called this "The Scale of Justice" and competing candidates would each mount a platform. The heaviest person, or whomevers platform came to rest closest to the ground was deemed the most grounded and therefore level headed and suitable to lead. Modern science allows us the insight that this meant the fattest would always win. Well, Jeor and his colossal thunder thighs (as so often described by GRRM in the books) broke the darned scale. Fattest leader in their history. And also why Jon was able to get elected democratically.