Born in Leeds and raised in Essex, Frain admits to having a fascination with performing from an early age. By the time he was in his teens, he was writing, directing and acting in his own plays. Frain held several odd jobs and traveled before enrolling in 1987 at the University of East Anglia as a theater major, originally with the intention of studying directing. In 1990, he auditioned for the Central School of Speech and Drama and switched to acting. Before he had completed the three-year program, Frain landed his first film role, as the troubled Oxford student who runs afoul of C S Lewis (Anthony Hopkins) in "Shadowlands" (1993). Additional work quickly followed including turns on the small screen as a suicidal Liverpudlian "rent boy" in "Prime Suspect 3" and a presumptuous lieutenant on the popular "Soldier, Soldier" (both 1993). His breakthrough role was as the cruel, closeted aristocrat in the BBC/PBS miniseries "The Bucanneers" (1995) and the actor acquitted himself as both the prime assassin in "Rasputin" (HBO, 1996) and in the title role of a 1997 experimental TV production of "Macbeth" that reset the tragedy in a contemporary housing project.
Frain displayed his softer side as Philip Wakem, the crippled childhood friend of Maggie Tulliver (Emily Watson), in the film adaptation of George Eliot's "The Mill on the Floss" (aired in the USA on PBS' "Masterpiece Theatre" in 1997). As the man who has loved the heroine, he proved a strong screen presence and he and Watson exhibited chemistry. The duo was reunited in the biopic "Hilary and Jackie" (1998), with Watson portraying the turbulent cellist Jacqueline du Pre and Frain cast as her husband, the Argentinean pianist-conductor Daniel Barenboim. The busy actor has continued to land roles that call upon him to display his versatility such as a lawyer who falls for his opposing counsel (Natascha McElhone) in the romantic comedy "What Rats Won't Do" (1998), his stunning turn the titular French filmmaker in Julien Temple's "Vigo - A Passion for Life" and as Ralph Fiennes' younger brother, a Hungarian Jew, in "Sunshine/The Taste of Sunshine" (both 1999).