He changed his name from Mladen Sekulovich to Karl Malden at age 22. He anglicized his first name by switching the letters and made it his last name and then took his uncle's first name. This was because the first theatre company he was in wanted him to shorten his name for the marquee. He thought they wanted to fire him and were using his name as an excuse, although this was not the case, so he changed it not to give them the excuse.
Malden often finds ways to say "Sekulovich" in films and television shows in which he appears. For example, as General Omar Bradley in Patton, as his troops slog their way through enemy fire in Sicily, Malden says "Hand me that helmet, Sekulovich" to another soldier. In Dead Ringer, as a police detective in the squad room, Malden tells another detective: "Sekulovich, gimme my hat." In Fear Strikes Out, Malden, playing Jimmy Pearsall's father John, introduces Jimmy to a baseball scout named Sekulovich. In Birdman of Alcatraz, as a prison warden touring the cell block, Malden recites a list of inmates' names, including Sekulovich. Malden's father was not pleased, as he told his son 'Mladen, no Sekulovich has ever been in prison!' Perhaps the most notable usage of his real name was in the TV series The Streets of San Francisco. Malden's character in the program, Mike Stone, employed a legman (played by Art Metrano) with that name, who did various errands.
He eventually traveled to New York City, and first appeared as an actor on Broadway in 1937. He did some radio work and in a small role made his film debut in They Knew What They Wanted. He also joined the Group Theatre, where he began acting in many plays and was introduced to a young Elia Kazan, who would later work with him on A Streetcar Named Desire (1951) and On the Waterfront (1954). His acting career was interrupted by World War II, during which he served as a noncommissioned officer in the 8th Air Force. While in the war, he was given a small role in the U.S. Army Air Forces play and film Winged Victory. After the war ended in 1945, he resumed his acting career, playing yet another small supporting role in the play Truckline Cafe, with a then-unknown Marlon Brando. He was given a co-starring role in the play All My Sons with the help of director Elia Kazan. With that success, he then crossed over into steady film work.
Malden resumed his film acting career in the 1950s, starting with The Gunfighter (1950) and Halls of Montezuma (1950). The following year, he starred in A Streetcar Named Desire (1951), playing Mitch, Stanley Kowalski's best friend who starts a romance with Blanche DuBois (Vivian Leigh). For this role, he won an Academy Award for Best Supporting Actor.
Other films during this period included On the Waterfront (1954), where he played a priest who influenced Terry Malloy (Marlon Brando) to testify against mobster-union boss Johnny Friendly (Lee J. Cobb). In Baby Doll (1956), he played a power-hungry sexual man who had been frustrated by a teenage wife. He starred in dozens of films from the late 1950s to the early 1970s, such as Fear Strikes Out (1957), Pollyanna (1960), Birdman of Alcatraz (1962), Gypsy (1962), How the West Was Won (1962), The Cincinnati Kid (1965), and Patton (1970), playing General Omar Bradley. After Summertime Killer (1972), he appeared in the made-for-television film The Hijacking of the Achille Lauro (1989) (as Leon Klinghoffer).
Malden's father was delighted about this series being in San Francisco, as he had intended to settle in that city, but had to change his plans as he'd arrived on the day of the San Francisco earthquake.
On Streets, Malden played a widowed veteran cop with more than 20 years of experience who is paired with a young officer recently graduated from college. During its first season, it was a ratings winner among many other 1970s crime dramas, and served as ABC's answer to such shows as Hawaii Five-O, Adam-12, Ironside, Barnaby Jones, Kojak, McMillan and Wife, Police Woman, The Rockford Files and Switch.
During the second season, production shifted from Los Angeles to San Francisco. For his work as Lt. Stone, Malden was nominated for a Primetime Emmy Award for Outstanding Lead Actor - Drama Series four times between 1974 and 1977, but never won. After two episodes in the fifth season, Douglas left the show to act in movies; Douglas had also produced the film One Flew Over the Cuckoo's Nest in 1975. Lt. Stone's new partner was Inspector Dan Robbins, played by Richard Hatch. The show took a ratings nosedive, and ABC canceled it after five seasons and 119 episodes.
In 1997, Malden published his autobiography, When Do I Start?, written with his daughter Carla.
On November 12, 2005, the United States House of Representatives authorized the U.S. Postal Service to rename the Los Angeles Barrington Postal Station as the Karl Malden Postal Station in honor of Malden's achievements. The bill, H.R. 3667, was sponsored by Representatives Henry Waxman and Diane Watson.
For his contribution to the motion picture industry, Karl Malden has a star on the Hollywood Walk of Fame at 6231 Hollywood Blvd. In 2005, he was inducted into the Western Performers Hall of Fame at the National Cowboy & Western Heritage Museum in Oklahoma City, Oklahoma.