The 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 season, 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.
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 last four seasons and equalled teammate Emma Kearney's record with her eighth blazer.
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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