In the period Darryl F. Zanuck was dominant at the 20th Century Fox Studio, from the 1930s through the 1960s, McLean was the studio's most prominent editor and ultimately the head of its editing department. She won the Academy Award for Best Film Editing for the film Wilson (1944). She was nominated for the same award another six occasions, including All About Eve (1950). Her total of seven nominations for Best Editing Oscar was not surpassed until 2012 by Michael Kahn.
She had an extensive collaboration with the director Henry King over 29 films, including Twelve O'Clock High (1949). Her impact was summarized by Adrian Dannatt in 1996 who wrote that McLean was "a revered editor who perhaps single-handedly established women as vital creative figures in an otherwise patriarchal industry."