The Crows avoided the wildcard finals after Walker and Izak Rankine (35 touches, four goals) starred in a 24.13 (157) to 15.11 (101) triumph on Saturday night.
Adelaide hold fifth spot overnight, but will slip to sixth should Hawthorn's expected win over lowly West Coast on Sunday eventuate.
Veteran forward Walker was playing his last home-and-away game for the Crows, after announcing his looming retirement.
And after a prolonged pre-game tribute, the 36-year-old kicked three goals in the initial 10 minutes to delight an adoring 52,332-strong Adelaide crowd.
"It just had a good feel about it," Crows coach Matthew Nicks said.
"You could just feel the atmosphere and emotion for our big man."
Rankine dazzled early, kicking two specials and creating two more goals, and Riley Thilthorpe bombed two accurate 55m set shots.
The Giants lost key backman Sam Taylor, ruled out with concussion after a knock in a marking contest.
GWS rallied in the second term with six goals to two and were 21 points down at halftime.
Jake Stringer, in his 250th AFL game and likely last with the Giants, booted three goals to halftime as the Crows lost small forward Zac Taylor to a hamstring injury.
Stringer slotted his fourth with another spectacular effort early in the third quarter and the visitors were only 16 points down.
But Adelaide rapidly responded, with Walker collecting two more majors and Josh Rachele slotting two in a minute.
Stringer potted his fifth goal late in term, but the Crows were a commanding 35 points up at three quarter-time, 17.8 to 10.9.
Rankine soon added another highlight to his monster game with a classy third goal - he also had 12 clearances and 10 score involvements.
His teammates Thilthorpe, Darcy Fogarty and Ben Keays also booted three majors each in Adelaide's highest score of the season.
Captain Jordan Dawson (32 disposals) was a standout, and Dan Curtin's 23 touches included five clearances and a goal.
The Giants, despite Stringer finishing with six goals and the efforts of Clayton Oliver (25 possessions), Lachie Ash (26) and Lachie Whitfield (21), end a disappointing season in 12th spot, with 10 wins and 13 losses.
"We have got work to do," Giants coach Adam Kingsley said.
"We still managed to beat some of the really good teams ... but were a bit too inconsistent, so we have got to find a solution."
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