Almost immediately after demobilisation, Thornton joined a repertory company. He appeared in the farce "The Party Spirit" in the West End alongside Robertson Hare and Ralph Lynn. His first credited screen role was in the film "Radio Cab Murder" (1954). After working on stage and in a few films during the 1950s, he became a familiar face on British television, specialising in comedy but initially starred in the TV series "William Tell" as Heinburgher in episode 23, "The Surgeon". He was a regular on "It's a Square World", and appeared in British sitcoms such as "Hancock" ("The Blood Donor", 1961), "Steptoe and Son", "Sykes", "The Goodies" and "Love Thy Neighbour". He appeared in the "Danger Man" episode "The Assassin" as Pepe in 1961, and as a tailor in "The Sentimental Agent" episode 'Scroll of Islam' (1963). He worked with Dick Emery, Benny Hill, Frankie Howerd, Harry Worth, Reg Varney and Spike Milligan in their comedy shows and appeared in five episodes of "Steptoe and Son" during its first run from 1962 to 1965, and appeared in the film "Steptoe and Son Ride Again" (1973) and the 1973 television Christmas special, 'The Party'.