On PBS, he was an abusive, secretly gay husband in 1995's The Buccaneers, based on Edith Wharton's novel. Then in Prime Suspect 3, he played an abused boy so traumatized by detectives' questions that he threw himself out a window.
Now, in George Eliot's The Mill on the Floss, Frain plays crippled Philip Wakem, who would do anything for childhood love Maggie Tulliver.
"What's been good is that every time I've done something it's been totally different than what I've done before," Frain says from a house he shares with friends in London.
His striking looks - jet black hair and piercing blue eyes - are decidedly Irish, although "all my genes are unusual," he jokes.
When he got the role of Philip Wakem, he picked up Eliot's novel "straight away," he says. "I had to get some tips. I was curious because when I read the screenplay, which went really well as a very intense kind of family drama, it was not what I was expecting." He thought a Victorian drama would be "very much more domestic" and was quite surprised at Eliot's book.
Frain studied acting at England's Central School of Speech & Drama, and there landed a role that unleashed a film career.
"I was still at drama school, and I went to an audition for a film and I got it, and the film turned out to be Shadowlands," he recalled. "That was about four years ago and that was my first job - this huge movie directed by Richard Attenborough. It was amazing."
That led to more work, including An Awfully Big Adventure in 1995, HBO's Rasputin in 1996 and several upcoming roles: He's made a romantic comedy about lawyers called What Rats Won't Do and a new Robinson Crusoe, directed by George Miller of Mad Max fame, to be released next year.
And Frain is most excited about his depiction of Jean Vigo, a '30s film director in Burning Up.
"He was an anarchist and a surrealist - a predecessor to the French New Wave," Frain says. "It's hard to remember that there was youthful rebellion before James Dean. But Vigo was creating a kind of subversive culture."
But Frain says it's really a romance about Vigo and his wife, played by French actress Romane Bohringer.
"It was an incredible script, very powerful." And perfectly in line with Frain's budding resume.