He was a Tony Award winning actor and was a four-time nominee for the Best Supporting Actor Academy Award, but never won. Rains was considered to be "one of the screen's great character stars" with an extraordinary voice who was, according to the All-Movie Guide, "at his best when playing cultured villains".
During his lengthy career he was greatly admired by many of his contemporaries such as Bette Davis, Vincent Sherman, Ronald Neame and Albert Dekker all of whom became close family friends. Rains also inspired many younger actors such as John Gielgud, Charles Laughton and Richard Chamberlain.
Although he had played the single supporting role in the silent, Build Thy House (1920), Rains came relatively late to film acting and while working for the Theatre Guild, he was offered a screen test with Universal Pictures in 1932. His screen test for A Bill of Divorcement (1932) for a New York representative of RKO was a failure but, according to some accounts, led to him being cast in the title role of James Whale's The Invisible Man (1933) after his screen test and unique voice was inadvertently overheard from the next room. His agent though, Harold Freedman, had a strong connection with the Laemmle family, who controlled Universal Studios at the time, and Whale himself had been acquainted with Rains in London and was keen to cast him in the role. According to his daughter, this was the only of his films he ever saw. He also did not go to see the rushes of the day's filming "because he told me, every time he went he was horrified by his huge face on the huge screen, that he just never went back again."
Rains signed a long term contract with Warner Bros. on 27 November 1935 with Warner able to exercise the right to loan him to other studios and Rains having a potential income of up to $750,000 over 7 years. He played the villainous role of Prince John in The Adventures of Robin Hood (1938). Roddy McDowall once asked Rains if he had intentionally lampooned Bette Davis in his performance as Prince John and Rains' only reply was "an enigmatic smile." Rains later revealed to his daughter that he'd enjoyed playing the prince as a homosexual, by using subtle mannerisms. Rains later credited the film's co-director Michael Curtiz with teaching him the more understated requirements of film acting, or "what not to do in front of a camera." On loan to Columbia Pictures, he performed the role of the corrupt American senator in Mr. Smith Goes to Washington (1939) for which he received his first Academy Award nomination as Best Supporting Actor. For his home studio, Warner Bros, he played the murderer Dr. Alexander Tower in Kings Row (1942) and the cynical police chief Captain Renault in
His only singing and dancing role was in a 1957 television musical version of Robert Browning's The Pied Piper of Hamelin, with Van Johnson as the Piper. The NBC colour special, broadcast as a film rather than a live or videotaped programme, was highly successful with the public. Sold into syndication after its first telecast, it was repeated annually by many local US TV stations.
Rains remained active as a character actor in the 1950s and 1960s, appearing in films and as a guest in television series. Two of his late screen roles were as Dryden, a cynical British diplomat in Lawrence of Arabia (1962) and King Herod in The Greatest Story Ever Told (1965), his last film. In CBS's Rawhide, he portrayed Alexander Langford, an attorney in a ghost town, in the episode "Incident of Judgment Day" (1963).
Jessica Rains remembered her father's work ethic: