He provided testimony to the House Un-American Activities Committee which led to the Hollywood blacklist in 1947.
McGuinness was born on December 20, 1894, in Drogheda, County Louth, Ireland,[1] and immigrated to New York in 1904.
[citation needed] McGuinness was one of the earliest editors and contributors at The New Yorker magazine; in the March 14, 1925, issue, he profiled the boxer Jack Dempsey and continued to contribute pieces (nonfiction, fiction, and poetry) until 1927.
[2] He relocated to Los Angeles in the late 1920s, at the dawn of the "talkies" era, and thereafter worked in the film industry as a writer and producer.
[citation needed] He eventually became chief supervisor and executive producer at Metro-Goldwyn-Mayer.