The 27-year-old centre has a wealth of experience, having played for Cardiff Blues before making a big impression during his time at Sale.
The big-tackling Welshman has spent the past two seasons in the Top 14 but he is now looking forward to teaming up with former Blues boss Dai Young at Wasps.
Thomas, who can also play at fly-half, told the club's official site: "I am delighted to be returning to England to be part of an exciting squad and coaching team.
"I have enjoyed my time in France but feel it is the right time to return to England and be closer to home.
"I know Dai Young well from my time at the Blues, and am looking forward to working with him again."
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Gilbert Blitz 8S rugby cleat is a great cleat at a great price of $69.99. Get a new pair of cleats today.
A cool looking all black rugby cleat with the high performance adidas is known for. Get in the Gear!
Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
The New Zealand All Blacks training jersey for 2013/14. Get in the Gear!
The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.