The Welsh rugby star exited the house to affectionate cheers from the Elstree audience.
Thomas had been tipped by many Digital Spy readers to win the Channel 5 reality show.
The 37-year-old received fewer votes than Denise Welch and Frankie Cocozza.
Putting a positive spin on his exit, he told Brian Dowling: "I think everybody's focus was to get to the last few days, and not to get voted out by the people in the house, so that's a massive achievement."
On why he was so popular in the house, he explained: "I tried to get on with everyone, I tried to be myself with everyone. I didn't try for people to like me, I just liked them.
"I'm a team player, I don't like to do things on my own, I'm not an individual. I wanted to be the team player [in the house]."
Michael Madsen and the Shannon twins left the house earlier tonight.
Watch Gareth Thomas's eviction from Celebrity Big Brother below: