Thomas is a successful rock and roll musician in Canada, with the height of his solo career during the 1970s with his most memorable hit being 1973's "Painted Ladies". Success in the American market, however, has proven to be elusive with the possible exception of "Painted Ladies", which remains his only U.S. Top 40 hit, and the song "Runner" which was recorded by Manfred Mann's Earth Band. He has also done musical composition for about a dozen films and television shows. Before breaking through with "Painted Ladies", he was a producer at the CBC. Before that, he was part of the folk music group Tranquility Base. In 1974, he won a Juno Award for "Most Promising Male Vocalist of the Year". That year he toured in eastern Canada with April Wine. In 1976 he signed with Chrysalis Records. In 1981, Thomas made a cameo appearance on SCTV with his real life older brother Dave Thomas during a sketch of "The Great White North". He played himself and performed the songs, "Pilot" and "Hold On". He also wrote and recorded the theme song for his brother's film Strange Brew. As well, Thomas was a musical guest on the CTV children's show Whatever Turns You On in 1979. Many of his songs have been covered by popular artists, including "Hold On", "The Runner", "Right Before Your Eyes", and "Chains". In 1988, Daryl Braithwaite had hits in Australia with two Thomas compositions: "As the Days Go By", and "All I Do". Bette Midler also covered his song "To Comfort You" on her Bette of Roses album. He is also known for the portrayal of the character "Dougie Franklin" on the Canadian comedy series The Red Green Show. From 1991 through 2002, Thomas released four albums with The Boomers. In 2009, Thomas provided the music for the animated seriesBob & Doug, based on the SCTV characters of the same name. He has written two books, Bequest, Canadian Best Seller, and The Lost Chord, both through Manor House Publishing. In 2010, Wounded Bird Records re-issued "Still Here" on CD. On 16 June 2014, Thomas was awarded the National Achievement Award by SOCAN at the 2014 SOCAN Awards in Toronto. In 2015, he performed with Darcy Hepner and the Hamilton Philharmonic Orchestra, and recorded with them for a CD. During the summer of 2016, Thomas was touring Ontario, Canada, with singers Murray McLauchlan, Cindy Church, and Marc Jordan, in the group Lunch At Allen's. The tour was continuing in late 2018 with a series of dates in Ontario. Thomas is a member of the Canadian charity Artists Against Racism.
