Born in Cologne, Rhine Province, Germany, Klemperer and his family fled Germany in 1935. After serving in the United States Army during World War II, he began his professional acting career on the Broadway stage in 1947. Klemperer appeared in several films and numerous guest starring roles during the 1950s and 1960s. In 1965, he won the role of Colonel Wilhelm Klink on the CBS television sitcom Hogan's Heroes. The series aired for six seasons with Klemperer receiving a Primetime Emmy Award for Outstanding Supporting Actor in a Comedy Series nomination for each year, winning the award in 1968 and 1969.
Klemperer was born in Cologne, Germany, to a musical family. His father was renowned conductor Otto Klemperer and his mother was soprano Johanna Geisler. He had a younger sister named Lotte (1923–2003). His father was Jewish by birth; he converted to Catholicism but later converted back to Judaism. His mother was Lutheran.
The Klemperer family emigrated to the United States in 1935, settling in Los Angeles, where Otto Klemperer became conductor of the Los Angeles Philharmonic. Werner Klemperer began acting in high school and enrolled in acting courses at the Pasadena Playhouse before joining the United States Army to serve in World War II. While stationed in Hawaii, he joined the Army's Special Services unit, spending the next years touring the Pacific entertaining the troops. At the war's end, he performed on Broadway before moving into television acting.
Klemperer was also a violinist and an accomplished concert pianist. He broadened his acting career by performing as an operatic baritone and a singer in Broadway musicals. He can also be heard as the Speaker in Arnold Schoenberg's Gurre-Lieder, in a 1979 live performance with the Boston Symphony Orchestra.
Klemperer's first major film role was as a psychiatrist in Alfred Hitchcock's The Wrong Man (1956). He then received significant notice for his role in the award-winning 1961 film Judgment at Nuremberg. The film presents a fictionalized account of the post-World War II Nuremberg Trials, with Klemperer portraying Emil Hahn, a Nazi prosecutor and one of the defendants at the trial. 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. He guest-starred in the first Brian Keith television series, Crusader, a Cold War drama that aired on CBS. During this time he made three guest appearances on Perry Mason: he played murder victim Stefan Riker in the 1958 episode "The Case of the Desperate Daughter"; the character Ulrik Zenas in the 1963 episode "The Case of the Two-Faced Turn-a-bout"; and Inspector Hurt in 1964 in "The Case of a Place Called Midnight". In 1963 Klemperer also portrayed a professor of psychology in "The Dream Book", an episode on the sitcom My Three Sons.
Prior to Hogan's Heroes, Klemperer appeared in the 1956 episode 'Safe Conduct' of Alfred Hitchcock Presents, along with future co-star John Banner; twice appeared as Hugo on the syndicated romantic comedy series, How to Marry a Millionaire (1957–1959), with Barbara Eden and Merry Anders; and appeared on the "Purple Gang" episode of The Untouchables.
He is best known, however, as Colonel Wilhelm Klink: the bumbling, cowardly and self-serving Kommandant of Stalag 13 on Hogan's Heroes, which aired from 1965–1971. Klemperer, conscious that he would be playing the role of a German officer during the Nazi regime, agreed to the part only on the condition that Klink would be portrayed as a fool who never succeeded. When Klemperer's father, the famous conductor, saw his first episode of Hogan's Heroes, he said to his son, "Your work is good . . . but who is the author of this material?" In addition to the character's bumblings, Klink was also remembered for his excruciating violin playing, spoofing Klemperer's talent for the violin. For his performance as Klink, Klemperer received six Emmy Award nominations for best supporting actor, winning in 1968 and 1969.
He appeared in character and costume as Klink in the Batman episode, "It's How You Play the Game" and as Officer Bolix in the Lost in Space episode "All That Glitters" in 1966. 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. 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 played a villain in an episode of Voyage To The Bottom Of The Sea titled "The Saboteur".
After Hogan's Heroes ended in 1971, Klemperer continued his career in stage and film roles and guest starring roles on television. In 1987, he portrayed Herr Schultz in the Broadway revival of Cabaret. The role earned Klemperer a Best Featured Actor Tony Award nomination. His final television work was a guest voice role in a 1993 episode of The Simpsons, as "Homer's Guardian Angel as Colonel Klink".
After his father's death in 1973, Klemperer expanded his acting career with musical roles in opera and Broadway musicals. He earned a Tony Award nomination for his performance in Cabaret in its 1987 Broadway revival. A member of the Board of Directors of the New York Chamber Symphony, Klemperer served as a narrator with many other American symphony orchestras including the Cincinnati Chamber Orchestra. 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. In 1981, he appeared, to critical and audience raves, as Prince Orlofsky in Seattle Opera's production of Die Fledermaus. In 1990 he narrated the children's story "Gerald McBoing Boing" (music by Gail Kubik) for a CD of classical music for children. In 1992, he made a guest appearance in an episode of Law & Order, "Starstruck," as the father of an attempted murder suspect.
In 1993, Klemperer reprised the role of Klink in an episode of The Simpsons as Homer's guardian angel and spirit guide in the episode "The Last Temptation of Homer" (episode # 5.9). According to the episode's DVD commentary, when Klemperer appeared, he had to be given a quick reminder of how to play Colonel Klink. He declined other offers to reprise the character, including one from talk show host Conan O'Brien.
Klemperer appeared in several episodes of the news/talk show Politically Incorrect.
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.
Klemperer was the father of two children, Mark and Erika, with his first wife, Susan Dempsay. On the set of Hogan's Heroes, he met his second wife, actress Louise Troy, who was making a guest appearance. They married in 1969, and divorced in 1975.
In 1997, Klemperer married his third wife, television actress Kim Hamilton, after dating her for 21 years. They remained married until Klemperer's death. Hamilton died 13 years later at age 81 on September 16, 2013.
Klemperer died of cancer according to John A. Anderson, his manager, on December 6, 2000, aged 80, at his home in Manhattan, New York City. He was cremated and his ashes were scattered at sea. He was survived by his wife Kim Hamilton and two children.