She was born Lois Ruth Hooker in Kitchener, Ontario. At age fifteen she ran away from home to join the Canadian Army during World War II. She became part of the Army Entertainment Corps, travelling Europe during the war performing music and dance numbers to entertain the troops. The truth about her age was discovered when the group reached London. In order to avoid court martial and deportation back to Canada, she enrolled at the prestigious Royal Academy of Dramatic Arts where she met fellow student Roger Moore.
Soon after travelling to Hollywood at the age of twenty, she won the Golden Globe Award, New Star Of The Year - Actress, for her role in the Shirley Temple comedy That Hagen Girl, as well as participating in a 1949 Life Magazine photo layout where she posed with Marilyn Monroe.
During the 1960s, she appeared in many television series and movies both in Britain and Canada, and was the star of Adventures in Rainbow Country later that decade. She guest starred in episodes of The Saint and The Persuaders! which both starred Roger Moore. Maxell also portrayed Miss Moneypenny in a 1967 made-for-television special (produced by EON Productions) titled, Welcome to Japan, Mr. Bond.
Director Terence Young, who once had turned Maxwell down, offered her the role of either Moneypenny or the recurring Bond girlfriend, Sylvia Trench. Maxwell was uncomfortable with a revealing scene the latter had in the screenplay, so she took the role as M's secretary. The Trench character was eliminated after From Russia with Love.