For Creighton, he made two films, and met John Grierson, who would become his mentor and life-long friend and colleague.

At the time, Grierson was a films officer at the Empire Marketing Board, a government agency which had been formed to encourage trade and national unity.

He brought Legg to Canada to make two films whose purpose was to promote the Dominion-Provincial Youth Training Program.

The films, The Case of Charlie Gordon and Youth Is Tomorrow, are regarded as milestones in the development of a mature, socially responsible documentary movement in Canada.

[7] Legg decided to stay in Canada, and became Director of Production for the Canadian Government Motion Picture Bureau.

He resigned from the NFB and convinced Legg to join him in New York, where he was able to reach a production deal with Universal Pictures.

Grierson's reputation was temporarily damaged when he was caught up in the Gouzenko Affair and accused of being a spy; the deal with Universal was cancelled and, in 1946, Legg returned to England.

[15] After retiring from filmmaking, Legg published four books: Trafalgar : An Eye-Witness Account of a Great Battle (1966),[16] Jutland: An Eye-witness Account of a Great Battle (1967),[17] The Heartland (1970, dedicated to Grierson and re-issued in 1991 as The Barbarians of Asia),[18] and The Railway Book: An Anthology (1988).