The 1946 film, starring James Stewart as suicidal George Bailey, beat Home Alone and The Muppet Christmas Carol in the poll.
It pushed Richard Curtis's romantic comedy Love Actually into second place, followed by the Will Ferrell movie Elf.
Family favourites The Muppet Christmas Carol and Home Alone took fourth and fifth place in the poll, carried out on RadioTimes.com.
Miracle On 34th Street and traditional Christmas films The Snowman and Scrooge also finished in the top 10.
Writing in the Radio Times, film critic Barry Norman said of It's A Wonderful Life: "Frank Capra's wonderful, life-enhancing film should be shown every Christmas, preferably after the Queen's Speech."
l RadioTimes.com top 10 Christmas films of all time (from 2172 votes):
1. It's a Wonderful Life (1946)
2. Love Actually (2003)
3. Elf (2003)
4. The Muppet Christmas Carol (1992)
5. Home Alone (1990)
6. National Lampoon's Christmas Vacation (1989)
7. Santa Claus: The Movie (1985)
8. Miracle On 34th Street (1994)
9. The Snowman (1982)
10. Scrooge (1951)