He won an Emmy Award for his convict turned lawyer character in Kaz (1978-79), a series which he also created and co-wrote. Leibman also picked up a Tony Award for his work in the Pulitzer Prize-winning play Angels in America. He is also widely known for his portrayal of Leonard Green, Rachel's overbearing father, on the sitcom Friends. Leibman had a recurring role on The Sopranos as Dr. Plepler.
Leibman was born in New York City, New York, the son of Grace (née Marks) and Murray Leibman, who worked in the garment business. He graduated in 1958 from Ohio Wesleyan University. He has been married to actress Jessica Walter since 1983. He was previously married to actress Linda Lavin (1969-1981). Leibman is Jewish.