The comedian has agreed a two-year deal after his success on the ITV1 talent show last year, The Sun reports.
Simon Cowell apparently insisted that Walliams commit to the Britain's Got Talent panel until 2014 as he didn't want to do the series without him.
The move is said to have affected the BBC's plan to make Walliams the face of its Saturday nights after bosses at the corporation expressed an interest in signing him up.
Walliams tells tonight's Jonathan Ross Show: "I've agreed to do two more. I can't wait. It's going to be a great series.
"Watching The X Factor now, I'm quite jealous that I'm not there because it's such a load of fun."
Cowell invited Walliams, Alesha Dixon and Amanda Holden to return next year immediately after May's final.
Watch Digital Spy's interview with Britain's Got Talent winners Ashleigh & Pudsey below: