The 28-year-old Welshman has been with Team Sky from the very outset back in 2010 and is one of eight British riders currently on the team roster.
In his first season for the team Thomas was one of the big success stories of the Tour de France, wearing the young rider's white jersey for most of the opening week.
After winning his second Olympic gold medal on the track at London 2012 he committed himself to the road and went on to play an integral part in Team Sky's second Tour de France victory, helping Chris Froome win the yellow jersey in 2013.
The talented all-rounder has again played a key role this season and will be a member of Team Sky until the end of 2016 after putting pen to paper on a new deal.
"I'm really happy to be staying with Team Sky for another two years," Thomas said. "I've been here since the start and I firmly believe it is the best place for me to fulfil my potential as a bike rider.
"I feel very supported here and I'm excited about what the future holds. I'll look forward to challenging myself both on and off the bike and striving to become the very best at what I do."
Team Principal Sir Dave Brailsford said: "We're delighted that Geraint has re-signed for another two years. He's been with Team Sky from the start and has been essential to the success that we've had.
"Team Sky has always been built around a strong British core, developing and nurturing home-grown talent to be the best they can be - and Geraint has been at the heart of that.
"On and off the bike Geraint is an influential member of Team Sky. Not only is he a strong character but he's one of a handful of world class riders that can do it all, whether that's on the climbs, flat, cobbles or time trials, which proves what a valuable member of the team he is.
"Over the last three weeks of the Tour de France Geraint has again underlined his qualities and has shown that he's an exceptional rider with an exciting future. He's a great guy, a good leader and we're delighted that he'll be a key part of the team going forward."
- Sports & Recreation
- Team Sky
- Tour de France