In front of more than 1,200 guests at Melbourne's Crown Palladium on Saturday night, Mitchell polled 177 votes to win the Peter Crimmins Medal from defenders Josh Gibson (160 votes) and Grant Birchall (138).
Rounding out the top five were Coleman medallist Lance Franklin (135 votes) and skipper Luke Hodge (126).
Mitchell collected votes in 20 of 23 matches, including five best on ground performances. The 28-year-old midfielder also won the Crimmins medal in 2006 and 2009, but rated himself a more rounded player in 2011.
"I think I was probably better defensively this year," Mitchell said.
"I worked pretty hard on that, particularly after the early part of the season where I got caught out a couple of times."
The award follows a season in which Mitchell polled 30 Brownlow Medal votes - a Hawks record - and was named All Australian for the first time.
Ineligible to win the Brownlow due to an early-season reprimand for a high bump on Geelong's Steve Johnson, his prolific vote-getting almost caused drama when he led late in the count.
But he was eventually overtaken by Collingwood's Dane Swan.
Mitchell admitted the possibility of missing out on the League's highest individual honour because of his minor indiscretion did play on his mind in the lead-up to the event.
"I tried to have a look at it on the day and work out how many I'd actually poll, because there'd been a few articles written about it," he said.
"I thought I'd probably poll about 20, which I didn't think would be enough.
"I certainly polled a lot more than I thought I would, but I don't think I deserved to be a Brownlow medallist on the season I had."
The 2008 premiership captain's year was all the more impressive considering his busy off-field life.
He began the season with three children under the age of one, including newborn twins.
Mitchell paid special tribute to his wife Lyndall for her support.
"It's meant a lot to me this year being able to go and play footy and really enjoy that part of my life, while having the kids at home who mean the world to me," he said.
Runner-up Gibson, in his second year at Waverley Park, was one of only two players to play every game.
He led the Hawks' injury-depleted backline following the losses of fellow key defenders Ben Stratton and Stephen Gilham.
The former Kangaroo was also adjudged the club's most consistent and best player in the finals.
Other awards
Best first year player - Paul Puopolo
Best clubman - Jordan Lewis
Most improved - Liam Shiels
Most consistent - Josh Gibson
Best player in finals - Josh Gibson
Peter Crimmins Medal top ten
1. Sam Mitchell - 177
2. Josh Gibson - 160
3. Grant Birchall - 138
4. Lance Franklin - 135
5. Luke Hodge - 126
6. Jordan Lewis - 125
7. Liam Shiels - 105
8. Cyril Rioli - 103
9. Brad Sewell - 102
10. Shaun Burgoyne - 86
