Schell rose to fame in various British film and television productions in the 1960s and 1970s. She acted under the name Catherine von Schell early in her career, but is best known by the name Catherine Schell.
Schell entered a convent school in the New York City borough of Staten Island. In 1957, Paul Schell joined Radio Free Europe and the family moved to Munich, where Catherine developed an interest in acting and attended the prestigious Falconberg School.
While filming The Amsterdam Affair in 1968 she met and married her first husband, the British actor William Marlowe (1932–2004) and moved to London.
In 1972, she appeared for the first time under the name Catherine Schell in Madame Sin, an American television movie starring Bette Davis. In 1975, she appeared opposite Peter Sellers in the comedy The Return of the Pink Panther as Lady Claudine Lytton. Her appearance in the film caused complications, as she would frequently break into uncontrollable laughter at the slightest prompting from Sellers. A scene in a hotel restaurant was shot many times unsuccessfully, and the final print of the film simply includes the footage of Schell attempting to stifle laughter at Sellers's behaviour. During the nightclub bar scene, Inspector Clouseau utters the line made famous by Humphrey Bogart, "Here's looking at you, kid", and Schell breaks character and leans forward in a fit of laughter.
Her marriage to Marlowe was dissolved in 1977 and she met the director Bill Hays. They married in 1982 and in 1984 worked together on the TV production of A Month in the Country.
In 1979, she appeared in a popular episode of the BBC series Doctor Who entitled City of Death as the Countess Scarlioni, wife of the episode's villain. The episode stars Tom Baker as the Doctor, with a cameo appearance by John Cleese and Eleanor Bron. She also played regular roles in other television series such as The Adventurer, One By One, Mog and Wish Me Luck, in addition to many other guest appearances, including The Persuaders!, The Troubleshooters, Arthur of the Britons, Return of the Saint, The Sweeney, The Onedin Line, The Gentle Touch, Lovejoy, Bergerac, The Bill and Howards' Way.