Schell rose to fame in various British film and television productions in the 1960s and 1970s. She acted under the name "Catherine von Schell" ("Schell" is the family name; "von Bauschlott" indicates the region of Germany from whence the Schell family originated) and "Katherina von Schell" early in her career, but is better known under the name "Catherine Schell".
Under the name Katherina von Schell she made her film debut in 1964 as the title character in the little-known German-language film Lana: Queen of the Amazons (German: "Lana - Königin der Amazonen").
In 1969, she appeared as Bond girl "Nancy" in the George Lazenby James Bond film On Her Majesty's Secret Service (credited as Catherina Von Schell), and as Clementine Taplin in the science fiction thriller Moon Zero Two.
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. It is frequently claimed that her tendency to break into uncontrollable laughter at Sellers's antics as inspector Clouseau ruined many takes. The final print of the film repeatedly shows Schell attempting to stifle laughter at Sellers's behaviour, both at the Lytton residence and during the nightclub bar scene. Although these scenes are frequently proffered as classic examples of corpsing, it is worth noting that Schell has maintained in interviews that she considered it in character for Lady Lytton to be amused at Clouseau, whom she does not see as a serious threat (an attitude made explicit during her banter with her husband at the film's climax in her hotel room).
Schell's first TV credit was 1967's Till Eulenspiegel, a comedy on West Germen TV where she played Nele and was billed as Katherina von Schell. Schell spent much of her career in television, and most of that on British television, with over 47 series spaning nearly 30 years. 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.
In addition to her career-defining work on Space: 1999, Schell is famous for another British sci-fi series appearance. In 1979, she appeared in a popular serial of the BBC series Doctor Who entitled City of Death as the Countess Scarlioni, wife of the episode's villain.
In 1975 Schell appeared in a first season episode of the ITC television science fiction series Space: 1999 entitled "The Guardian of Piri", playing the guardian's robotic servant. She returned as a regular cast member in the second season in the role of Maya the alien "metamorph" from the planet Psychon, perhaps her most popular character.