Initially, Mackenzie worked on television plays, following his apprenticeship with Loach. During this period he directed episodes of "The Jazz Age" and "ITV Saturday Night Theatre". His first film was the television drama "There Is Also Tomorrow" (1969), followed by two feature films "One Brief Summer" (1970) and "Unman, Wittering and Zigo", an adaptation of Giles Cooper's radio play (1971). Mackenzie still largely worked for television, aside from the independent production "Made" (1972), until in 1979 he directed the highly acclaimed "A Sense of Freedom", a BAFTA-nominated film (released on television in the US in 1985). "Freedom" was surpassed, however, by Mackenzie's next film, the gangster piece "The Long Good Friday", generally accepted as his masterpiece.