He produced a small body of prints during the 1920s and early 1930 and a series of line engravings by him were used in poster advertisements for Johnnie Walker whisky. A wood engraving entitled 'Landscape' by McNab is illustrated in Artwork, January 1926. In the 1930s, McNab moved to the USA and from 1938 to 1945 was the design director for Norman Bel Geddes (1893-1958) who was an American theatrical impresario and aeronautical design engineer. He was then appointed art director for Life magazine (1945-50) and subsequently worked in art museum administration including as a director of the Lowe Gallery (1950-55), assistant director of the Art Institute of Chicago (1956-57) and art consultant to the Mayo Foundation from 1967. He later lived in Savannah, Georgia. In 1932, he married the Australian-born film actress and wallpaper designer Dorothy Cumming (1894-1983). His second wife was Marjorie Kreilick who was not only a sculptor but held the post of Professor of Art at the University of Wisconson from 1953-1991.
With thanks to artbiogs.co.uk