Born in Stockholm, Gentele studied from 1944 until 1946 at the Dramatens elevskola, beginning a brief career as a film actor not long afterwards. He soon turned to directing, working for a time at the Royal Dramatic Theatre and then at the Royal Swedish Opera, where his more notable productions included Gian Carlo Menotti’s The Consul and Karl-Birger Blomdahl’s Aniara. He became director of the company in 1963.
He also directed films during approximately the same period (1947 to 1969), making at least 15 feature films and television movies. His 1951 film Leva på ‘Hoppet’ was awarded the Silver Bear for comedy at the Berlin International Film Festival.
He succeeded Sir Rudolf Bing as director of the Metropolitan Opera in New York City in 1972. Soon after assuming the post, on 18 July 1972, Gentele died in an automobile accident while on vacation in Sardinia; he was killed along with two of his daughters when the car in which they were riding collided head-on with a truck. A third daughter was injured, as was Gentele’s wife, Marit. Schuyler Chapin, Gentele’s assistant, was named acting director almost at once.