Runner-up to Adelaide's Ebony Marinoff last year, Riddell polled 23 votes to add the league's highest individual honour to her fifth All-Australian selection.
Geelong's Georgie Prespakis (20 votes) was second and Melbourne's Tyla Hanks (18) third in best-and-fairest polling, with West Coast's Ella Roberts (fourth).
North Melbourne star Jasmine Garner and Sydney's Laura Gardiner (15) were tied for fifth.
Sydney's explosive young gun Zippy Fish won the Rising Star award with a maximum 50 votes, ahead of Carlton's Poppy Scholz (23) and West Coast's Lucia Painter (23).
Riddell is the first North Melbourne player to win the best-and-fairest award in the league's 10 seasons and will lead the Kangaroos in Saturday's grand final against the Brisbane Lions.
The 29-year-old ball-magnet has enjoyed an outstanding 2025 campaign, in which she was also named the AFL Coaches Association's champion player of the year.
Riddell has broken her own AFLW record for most disposals in a game three times this season and amassed 40 or more possessions on five occasions, averaging a league-best 35.3 disposals per match.
"I'm very lucky and a little bit anxious to be up here," Riddell said as she accepted her prize at the AFLW Awards ceremony on Monday night.
"I'm surrounded by so many good players. I'm really humbled to be up here."
Remarkably, Riddell was overlooked in two drafts before being picked up by North Melbourne for their first season as an AFLW expansion club in 2019.
She has since gone on to become a club champion, premiership player and now a league best-and-fairest winner.
Riddell's winning tally included votes in nine games, and she was named best afield six times in a dozen appearances.
However, she didn't poll a vote in rounds six or eight, when she set new disposal records with 44 and 45 touches respectively.
Riddell, who has featured in every game of North Melbourne's record 26-match winning streak, paid tribute to her teammates and coach Darren Crocker in her acceptance speech.
"Crock does such an amazing job with the group and he's really big on just enjoying the journey," Riddell said.
"I think we do that each week. We don't look too far ahead and we're just so connected as a group.
"We love hanging out off-field as well and it just brings us so much closer together on-field.
"We have a strong system that we trust as a group and we don't try to be remarkable, we just try to be reliable in games, and trust each other along the way."
Minor premiers North were the best-represented club in the All-Australian team, with Riddell selected alongside teammates Garner, Tahlia Randall and Blaithin Bogue.
Garner was named All-Australian captain for the third time in the past four seasons and equalled teammate Emma Kearney's record with her eighth blazer.
"I'm absolutely honoured," Garner said. "It's pretty special.
"I love what I do. I'm so lucky and I'm just trying to enjoy the ride."
Bogue was one of a record four Irish players named in the All-Australian team along with Jennifer Dunne (Brisbane), Niamh McLaughlin (Gold Coast) and Aine McDonagh (Hawthorn).
Dunne and pocket rocket Courtney Hodder were the only two All-Australian representatives for the Lions, who will attempt to end North Melbourne's 26-game winning streak in the grand final.
Richmond's Sarah Hosking won mark of the year for her courageous, back-with-the-flight effort against Collingwood.
Sydney's Montana Ham won goal of the year for her run and finish against the Magpies.
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