Badel's earliest film role was as John the Baptist in the Rita Hayworth version of Salome (1953), a version in which the story was altered to make Salome a Christian convert who dances for Herod in order to save John rather than have him condemned to death. He portrayed Richard Wagner in Magic Fire (1955), a biopic about the Composer. He also played the role of Karl Denny, the impresario, in the film Bitter Harvest (1963). Around the same time, he played opposite Vivien Merchant in a television version of Harold Pinter's play The Lover (also 1963) and as Edmond Dantès in a BBC television adaptation of Alex Andre Dumas' The Count of Monte Cristo (1964).
Badel also played the villainous sunglasses-wearing Najim Beshraavi in Arabesque (1966) with Gregory Peck and Sophia Loren. He played the French Interior Minister in The Day of the Jackal (1973), a political thriller about the attempted assassination of President Charles de Gaulle; in the political television drama Bill Brand (1976) he played David Last, the government's Employment Minister, a left-wing former backbench MP who had recently joined the front bench after 30 years in the House of Commons. One of his last roles was that of Baron Nicolas de Gunzburg in the Paramount film Nijinsky (1980). A television adaptation for the BBC of The Woman in White (1982) by Wilkie Collins, in which Badel played the role of Count Fosco, was shown posthumously.