Klemperer then appeared in several films during his early acting career such as The Wrong Man (1956), Judgment at Nuremberg (1961), and Houseboat (1958), and numerous roles on television shows such as Alfred Hitchcock Presents (1956), Perry Mason (1957), Maverick (1957), Gunsmoke (1958), The Untouchables (1960), and Have Gun – Will Travel (1961), prior to his Hogan's Heroes role.

While stationed in Hawaii, he joined the Army's Special Services unit, spending the next years touring the Pacific entertaining the troops.

Prior to this, he had a small role in the 1957 Errol Flynn film Istanbul and a pivotal part in the "Comstock Conspiracy" episode of Maverick that same year.

He played the title role in the 1961 film Operation Eichmann, opposite his future co-star John Banner.

He is best known, however, as Colonel Wilhelm Klink: the bungling, cowardly, conceited, and self-serving Kommandant of Stalag 13 on Hogan's Heroes, which was broadcast on CBS from 1965 to 1971.

Klemperer, conscious that he would be playing the role of a German officer during the Nazi regime, accepted the part only on the condition that Klink would be portrayed as a fool who never succeeded.

He played a bumbling East German official in the 1968 American comedy film The Wicked Dreams of Paula Schultz, directed by George Marshall and starring Elke Sommer and several of his costars from Hogan's Heroes, including Bob Crane and John Banner.

Klemperer later starred in Wake Me When the War Is Over in 1969, playing the role of a German major, Erich Mueller, alongside Eva Gabor.

He also made occasional guest appearances on television dramas, and took part in a few studio recordings, notably a version of Arnold Schoenberg's Gurre-Lieder with the Boston Symphony and Seiji Ozawa, in 1979.

From 1979 to 1982, he appeared as Bassa Selim in 18 performances of Mozart's Singspiel Die Entführung aus dem Serail at the Metropolitan Opera in New York.

[8] In 1981, he appeared, to critical and audience raves, as Prince Orlofsky in Seattle Opera's production of Die Fledermaus.

In January 1991 he performed as narrator in the Milwaukee Symphony Orchestra's concerts and subsequent Koss Classics recording of "Lelio", by Hector Berlioz, in an English translation.

[9] For many years, Klemperer was an elected member of the council of Actors' Equity Association, and was a vice president of the union at the time of his death.