Thomas trained at RADA where he also became an associate member. His many stage appearances included Twelfth Night, Othello and Anna Christie with the RSC, and productions of Educating Rita, Cat on a Hot Tin Roof and The Crucible.
His other TV appearances included Z-Cars, Bergerac and Torchwood. He was twice nominated for a BAFTA for his performances in Stocker's Copper and Morgan's Boy (1984).
A host of theatrical figures have paid tribute to the actors on twitter including Samuel West who said: "Sad to hear Gareth Thomas, star of Blake's 7 and Children of the Stones has died. Taught me what leadership was. Diolch o galon. Siwrne dda."
Sad to hear Gareth Thomas, star of Blake's 7 and Children of the Stones has died. Taught me what leadership was. Diolch o galon. Siwrne dda.
— Samuel West (@exitthelemming) April 14, 2016
Very sad to hear of the death of my good friend Gareth Thomas. We were at RADA then Blakes 7 and onwards. He was a proud Welshman. RIP.
— Stephen Greif (@StephenGreif) April 14, 2016
Very sorry to hear of the death of Gareth Thomas. A lovely man, a damn fine actor and a childhood hero to millions. pic.twitter.com/6eFy4hCvRr
— Barnaby Edwards (@BarnabyEdwards) April 14, 2016