The Little Britain star features alongside Cowell, Amanda Holden, and Alesha Dixon on the judging panel of the competition, and the eighth season of the U.K. show begins on Saturday (12Apr14).
Walliams has now revealed he leaped into action while filming the show to rescue Cowell as the record label boss began to choke on a snack in between takes.
Walliams tells British talk show host Alan Carr, "In the show I actually give Simon the Heimlich manoeuvre... He's always eating something whilst the contestants come on. It's normally orange pieces or mints and he choked on the mint and I actually saved his life and I do regret that!"
Holden adds, "He (Cowell) was seriously choking and David came up behind him and dry humped him! He did the Heimlich manoeuvre. It worked anyway!"