The trio from Sydney defeated Greg Gould and The Chase for the top prize of $250,000.
Brisbane dance crew Academy of Brothers were eliminated third.
Uncle Jed’s Laura Stitt and cousins Danny and Shannon Stitt captivated from their first appearance in the very first episode, with a mix of funk, soul, reggae and jazz.
“It’s been an incredible ride! Thanks for all your support and for getting us this far!” they posted on Facebook.
Nine’s series has struggled to pop this season, with Seven counter-programming The X Factor against its own former show.
The Live Decider included performances from judges Timomatic and Geri Halliwell.