LONDON — As accusations of anti-Semitism plague the British Labour Party and its leader, Jeremy Corbyn, the party has a prominent new voice as it tries to steady the ship: a comedian better known for his whimsical stand-up shows and appearances in Hollywood movies.

The comedian, Eddie Izzard, who has described himself as “a straight transvestite,” took a seat this week on Labour’s governing body, after his predecessor was forced to quit over her support for a candidate accused of Holocaust denial.

Mr. Izzard, 56, may be known for laughs, but he is serious about politics, a longtime Labour supporter who has run for a position on the party’s National Executive Committee twice before.

“We must stamp out completely the stain of anti-Semitism,” he said. “I have campaigned against hate my whole life and will continue to do so wherever it rears its ugly head.”