Born Stefan Ihnat, he was raised on a farm in Lynden, Ontario. His family settled there after fleeing his native Czechoslovakia in 1939, when he was five years old. Ihnat, his mother, father, and two young boys from other families left Czechoslovakia three days before Prague was occupied by invading German forces in March of that year.  Ihnat became hooked on acting when he played a child role in an amateur theatre near Lynden. He said, “I knew this was the only thing I wanted to do with my life.” He also said “I think wanting to act started when I was about 14 as an escape valve to my environment. I was raised on a farm and I decided I wanted to be everything in life. Acting is the best way to do it.”  Ihnat moved to the United States in 1958 to pursue a career in acting and attended the Pasadena Playhouse. He gained United States citizenship. At a time when he had difficulty finding work he enlisted in the U.S. Army for two years and served at Headquarters and Headquarters U.S. Army, Port Inchon, South Korea. In 1960, Pvt. Ihnat won second prize in the Republic of Korea poetry contest for his entry titled “Toil in the Night.”  Ihnat guest-starred in several television series during the 1960s. As an actor, he first achieved wide notice for his portrayal of a mind-controlled lieutenant in the science fiction television series The Outer Limits. His extended speech at the end of that double episode, (“The Inheritors”, (1964), is one of the most affecting moments in television. Ihnat eventually became one of the most in-demand A-list guest stars of the 1960s. In 1965 he guest starred as murderer Charlie Parks in the Perry Mason episode, “The Case of the Duplicate Case.”

Ihnat held over seventy guest credits in such well known series as Star Trek episode “Whom Gods Destroy” (1969) as the psychotic Garth of Izar and also two episodes of The Fugitive, entitled “Cry Uncle” (alongside Ron Howard) and “The Walls of Night”. Other credits include Blue Light (“Field of Dishonor”), Gunsmoke (“Exodus 21:22”, “Jenny” with Lisa Gerritsen (December 28, 1970), and “Noose of Gold”), The Silent Force (“Take As Directed For Death”), Bonanza (“A Dream to Dream” and “Terror at 2:00”), The Virginian (“Jed” and “Last Grave at Socorro Creek”), Mission: Impossible (“The Mind of Stefan Miklos”), Cimarron Strip (“The Hunted”), I Dream of Jeannie (“My Master the Rainmaker”), Mannix (“End Game” and “To Catch the Lightning”), The F.B.I. (“Region of Peril” and “The Prey”), The Name of the Game (“The Chains of Command” and “Nightmare”), Medical Center (“Fright and Flight”) and Perry Mason (“The Case of the Duplicate Case”).

Ihnat had several guest roles in Mission: Impossible including the brilliant Soviet Union investigator Stefan Miklos in the 1969 episode “The Mind of Stefan Miklos,” widely praised as one of the most cerebral and intelligent episodes of the entire series. While he played other roles (mostly villains) in the show, his performance in this episode is his most memorable.

From 1964 to 1968 he appeared in eight feature films. He often played villains, using his abilities to subtly turn one-dimensional characters into complex and multi-dimensional antagonists. In 1967, Lamont Johnson cast him in the film Kona Coast in which Ihnat played a murderous playboy in Hawaii doping up teenagers and causing mayhem to the property and person of the character played by lead actor Richard Boone. In 1968, he memorably portrayed a murderous thug in the film Madigan, starring Richard Widmark and Henry Fonda and a NASA administrator in the film Countdown, directed by Robert Altman and starring James Caan and Robert Duvall. Other films of note during this period included In Like Flint and Hour of the Gun.

Ihnat was a screenwriter and director as well. He wrote, produced and starred in “Do Not Throw Cushions Into The Ring,” which while never released, led to his receiving the plum position of directing The Honkers, starring James Coburn, with whom he had appeared in In Like Flint. He also co-wrote the movie with Stephen Lodge.  Steve Ihnat was married to Sally Carter-Ihnat who had been a Playboy Playmate of the Month in May 1962. Sally had a daughter from a previous marriage. Steve’s son, Stefan, was born one month before Ihnat died. At the age of thirty-seven, he suffered a heart attack while visiting the Cannes Film Festival in France, where he was promoting his “Do Not Throw Cushions in the Ring.” He died on his wife’s 30th birthday, while his death was announced on the Emmys telecast.  Ihnat is interred in the Westwood Village Memorial Park Cemetery in Los Angeles. His son, Stefan, who died at age 32 from complications connected with diabetes, is interred next to him.