McDowell is known for the roles of Alex DeLarge in Stanley Kubrick's "A Clockwork Orange" (1971), the title character in "Caligula" (1979), and Mick Travis in the trilogy of "if..." (1968), "O Lucky Man!" (1973), and "Britannia Hospital" (1982). He has appeared in films such as "Time After Time" (1979), "Cat People" (1982), "Star Trek Generations" (1994), "Tank Girl" (1995), "Gangster No. 1" (2000), "Easy A" (2010), "The Artist" (2011) and "Bombshell" (2019). He also appeared as Dr. Samuel Loomis in the 2007 remake "Halloween" and its 2009 sequel, "Halloween II".