[4] Martell received his first film credit as musical director in 1949 on Val Guest's Murder at the Windmill and was both musical director and composer of the film score to Guest's Miss Pilgrim's Progress (1950).
He succeeded John Hollingsworth as musical director after Hollingsworth's death in 1963, and also composed the scores to the 1966 Lindsay Shonteff film Run with the Wind , the 1968 Hammer film The Anniversary, starring Bette Davis and (with Don Ellis) Moon Zero Two (1969).
Like his colleagues Ernest Irving (at Ealing), Muir Mathieson (at Denham) and Hubert Clifford (at the London Film Studios), Martell engaged a wide variety of leading musicians to contribute scores, including classical concert music composers still young and not yet skilled in film music, such as Don Banks, Richard Rodney Bennett, Wilfred Josephs, John McCabe, Paul Patterson, and Malcolm Williamson.
[2][6] He also engaged more experienced film composers such as Malcolm Arnold, Elisabeth Lutyens and James Bernard.
[2] Martell also composed TV music and conducted the London Casino Orchestra.