The FA Cup winners, who beat Manchester City at Wembley Stadium, will play in the Championship next season after defeat to Arsenal, following an eight-year stay in the top flight
Roberto Martinez's side went into the clash with the Gunners knowing only a victory would keep any realistic survival chances alive going into the final day of the season.
But, despite Shaun Maloney pulling his side level after a Lukas Podolski opener going into half time, Arsenal ran rampant after the break, scoring three in quick succession to send Wigan into the Championship.
The Latics were well in the game up to Walcott's 63rd minute goal with Arouna Kone missing a big chance to put Wigan ahead just after half-time.
But three goals in eight minutes condemned the FA Cup winners to the second tier for the first time in eight years, joining Reading and QPR in the Championship.
Wigan will host their final league game of the season on Sunday against Aston Villa, in what could be Roberto Martinez's final game at the DW Stadium after being linked as David Moyes's successor at Everton.