In 1932, Stander landed his first credited film role in the Warner-Vitaphone short feature In the Dough, with Fatty Arbuckle and Shemp Howard. He made several other shorts, the last being The Old Grey Mayor with Bob Hope in 1935. That year, he was cast in a feature, Ben Hecht's The Scoundrel with Noel Coward. He moved to Hollywood and was signed a contract with Columbia Pictures. Stander was in a string of films over the next three years, most notably in Frank Capra's Mr. Deeds Goes to Town (1936) with Gary Cooper and Meet Nero Wolfe (1936), and A Star Is Born (1937) with Janet Gaynor and Fredric March.
Stander's distinctive rumbling voice, tough-guy demeanor, and talent with accents made him a popular radio actor. In the 1930s and 1940s he was on the Eddie Cantor Show, Bing Crosby's KMH show, the Lux Radio Theater production of A Star Is Born, The Fred Allen Show, the Mayor of the Town series with Lionel Barrymore and Agnes Moorehead, Kraft Music Hall on NBC, Stage Door Canteen on CBS, the Lincoln Highway Radio Show on NBC, and The Jack Paar Show, among others. In 1941 he originated the title role of The Life of Riley on CBS, later made famous by William Bendix. Stander played the role of Spider Schultz in both Harold Lloyd's 1936 film The Milky Way and its 1946 remake starring Danny Kaye, The Kid from Brooklyn. He was a regular on Danny Kaye's zany comedy-variety radio show on CBS (1946–1947), playing himself as "just the elevator operator" amidst the antics of Kaye, future Our Miss Brooks star Eve Arden, and bandleader Harry James.
Strongly liberal and pro-labor, Stander espoused a variety of social and political causes, and was a founding member of the Screen Actors Guild. At a SAG meeting held during a 1937 studio technicians' strike, he told the assemblage of 2000 members, "With the eyes of the whole world on this meeting, will it not give the Guild a black eye if its members continue to cross picket lines?" (The NYT reported: "Cheers mingled with boos greeted the question.") Stander also supported the Conference of Studio Unions in its fight against the Mob-influenced International Alliance of Stage Employees (IATSE). Also in 1937, Ivan F. Cox, a deposed officer of the San Francisco longshoremen's union, sued Stander and a host of others, including union leader Harry Bridges, actors Fredric March, Franchot Tone, Mary Astor, James Cagney, Jean Muir, and director William Dieterle. The charge, according to Time magazine, was "conspiring to propagate Communism on the Pacific Coast, causing Mr. Cox to lose his job."
In 1938, Columbia Pictures head Harry Cohn allegedly called Stander "a Red son of a bitch" and threatened a $100,000 fine against any studio that renewed his contract. Despite critical acclaim for his performances, Stander's film work dropped off drastically. After appearing in 15 films in 1935 and 1936, he was in only six in 1937 and 1938. Then he was in just six movies from 1939 through 1943, none made by major studios, the most notable being Guadalcanal Diary (1943).
Stander appeared in no movies in 1944 and 1945; then, with HUAC's attentions focused elsewhere due to World War II, he played in a number of mostly second-rate pictures from independent studios through the late 1940s. These include Ben Hecht's Specter of the Rose (1946); the Preston Sturges comedies The Sin of Harold Diddlebock with Harold Lloyd (1947) and Unfaithfully Yours with Rex Harrison (1948); and Trouble Makers with The Bowery Boys (1948).
HUAC returned its attention to Hollywood in 1947. That October, Howard Rushmore, who had belonged to the CP in the 1930s and written movie reviews for the Daily Worker, testified that writer John Howard Lawson, whom he named as a Communist, had "referred to Lionel Stander as a perfect example of how a Communist should not act in Hollywood." Stander was again blacklisted from movies, though he played on TV, radio, and in the theater.
In March 1951, actor Larry Parks, after pleading with HUAC investigators not to force him to "crawl through the mud" as an informer, named several people as Communists in a "closed-door session", which made the newspapers two days later. He testified that he knew Stander, but didn't recall attending any CP meetings with him.
At a HUAC hearing in April 1951, actor Marc Lawrence named Stander as a member of his Hollywood Communist "cell", along with actor Lester Cole and screenwriter Gordon Kahn. Lawrence testified that Stander "was the guy who introduced me to the party line", and that Stander said that by joining the CP, he'd "get to know the dames more"--which Lawrence, who didn't enjoy movie-star looks, thought a good idea. Upon hearing of this, Stander shot off a telegram to HUAC chair John S. Wood, calling Lawrence's testimony that he was a Communist "ridiculous" and asking to appear before the Committee, so he could swear to that under oath. The telegram concluded: "I respectfully request an opportunity to appear before you at your earliest possible convenience. Be assured of my cooperation." Two days later, Stander sued Lawrence for $500,000 for slander. Lawrence left the country ("fled", according to Stander) for Europe.
After that, Stander was blacklisted from TV and radio. He continued to act in the theater, and was in a 1953 revival of Pal Joey on Broadway and on tour.
"I am not a dupe, or a dope, or a moe, or a schmoe...I was absolutely conscious of what I was doing, and I am not ashamed of anything I said in public or private."An excerpt from that statement was engraved in stone for "The First Amendment Blacklist Memorial" by Jenny Holzer at the University of Southern California.
Other notable statements during Stander's 1953 HUAC testimony:
"[Testifying before HUAC] is like the Spanish Inquisition. You may not be burned, but you can't help coming away a little singed." "I don't know about the overthrow of the government. This committee has been investigating 15 years so far, and hasn't found one act of violence." "I know of a group of fanatics who are desperately trying to undermine the Constitution of the United States by depriving pacifists and others of life, liberty, and pursuit of happiness without due process of law." "...I don't want to be responsible for a whole stable of informers, stool pigeons, and psychopaths and ex-political heretics, who come in here beating their breast and say, 'I am awfully sorry; I didn't know what I was doing. Please--I want absolution; get me back into pictures.'" "My estimation of this committee is that this committee arrogates judicial and punitive powers which it does not possess."
Life improved for Stander when he moved to London in 1964 to act in Bertolt Brecht's St. Joan of the Stockyards, directed by Tony Richardson, for whom he'd acted on Broadway, along with Christopher Plummer, in a stillborn 1963 production of Brecht's The Resistible Rise of Alberto Ui. In 1965, Richardson broke the Hollywood blacklist for Stander by casting him in the black comedy about the funeral industry, The Loved One (film), based on the novel by Evelyn Waugh (who disavowed the movie), with an all-star cast including Jonathan Winters, Robert Morse, Liberace, Rod Steiger, Paul Williams and many others. In 1966, Roman Polanski memorably cast Stander in his only starring role, as the thug Dickie in Cul-de-Sac, opposite Françoise Dorléac and Donald Pleasence.
Stander stayed in Europe and eventually settled in Rome, where he appeared in many spaghetti Westerns, most notably playing a bartender named Max in Sergio Leone's Once Upon a Time in the West. In Rome he connected with Robert Wagner, who cast him in an episode of It Takes a Thief that was shot there. Stander's few English-language movies in the 1970s include The Gang That Couldn't Shoot Straight with Robert De Niro and Jerry Orbach, Steven Spielberg's 1941, and Martin Scorsese's New York, New York with Liza Minnelli and Robert De Niro.