Following his discharge from the U.S. Army at the end of World War II in 1945, he attended New York University, obtaining a degree in radio arts in 1947.

Harry Shapiro in Stalag 17,[5] subsequently playing the same role in the film version directed by Billy Wilder,[4] earning the Theater Owners of America's Laurel Award for outstanding comedy performance and best possibility for stardom.

However, the role of Harry Shapiro as portrayed by Lembeck was significant, as it demonstrated the resiliency of the average American under the extreme duress as a prisoner of war during WWII.

[5] In the 1961-1962 television season, Lembeck played a theatrical agent, Jerry Roper, in the ABC sitcom The Hathaways, starring Peggy Cass and Jack Weston as "parents" to the performing Marquis Chimps.

[4] Having spent a great deal of his adult life in uniform, Lembeck once again donned Navy togs in the 1962–1963 season to co-star with Dean Jones in the NBC sitcom Ensign O'Toole.

[4] He co-starred with Steve McQueen in Love with the Proper Stranger and then spent part of the early 1960s playing the lovable bad guy malaprop Eric Von Zipper in six American International beach party films, with Frankie Avalon and Annette Funicello.

[citation needed] During the late 1960s and 1970s, Lembeck became a mainstay on television, making over 200 guest appearances, including Ben Casey, Mr. Novak, The Munsters, The Man from U.N.C.L.E., Route 66, The Monkees, Night Gallery, It Takes a Thief, The Partridge Family, Chico and the Man, Vega$, All in the Family, Hawkins, Batman and Mork & Mindy.

[4] Lembeck also directed the road companies of Stalag 17 and Mister Roberts, along with the revues A Night at the Mark in San Francisco and Flush in Las Vegas.

Lembeck was guest starring in an episode of Mork & Mindy when he suffered a heart attack, collapsed as he was leaving the set and died.