He dropped out of high school to work at a ballroom in Cedar Point, Ohio, running errands for the musicians performing there. He later worked as an electrician, cook, carnival worker and taxi driver. In 1946, he met record store owner and discographer Orin Blackstone in New Orleans and began assisting him in researching and compiling Blackstone's multivolume Index to Jazz. McCormick became Texas correspondent for Down Beat in 1949. He developed an interest in blues and began traveling and researching the lives and origins of undocumented blues musicians around the country and learning about folk traditions and customs.
In the late 1950s, McCormick "discovered" and recorded Mance Lipscomb, Robert Shaw and Lightnin' Hopkins. At the 1965 Newport Folk Festival, he assembled a group of former convicts who had never performed together, and after trying but failing to get Bob Dylan to end his rehearsals with members of the Paul Butterfield Blues Band, cut off Dylan's electricity supply, possibly giving rise to the apocryphal story that Pete Seeger had attempted to cut off the power during Dylan's debut performance with electric guitars and keyboards.
McCormick wrote numerous magazine articles and album liner notes and assembled an extensive private archive of Texas musical history. He researched the lives of dead blues musicians, such as Robert Johnson and Henry Thomas. He began research on Johnson in 1972, while working for the Smithsonian Institution, and interviewed people who had known the musician. McCormick originally intended to publish his research as a book, Biography of a Phantom, but he never completed it, and he later said that he had lost interest in it. His unfinished research with Paul Oliver on Texas blues was published in 2019 by Texas A&M University Press as The Blues Come to Texas.
- "Mack McCormick, Student of Texas Blues, Dies at 85". The New York Times. Retrieved November 26, 2015.
- Russell, Tony (1997). The Blues: From Robert Johnson to Robert Cray. Dubai: Carlton Books Limited. p. 166. ISBN 1-85868-255-X.
- Russell, p. 64
- Russell, p. 207
- Searching for Robert Johnson, Frank Digiacomo, Vanity Fair, November 2008]. Retrieved November 28, 2015.
- "The Blues Come to Texas". Texas A&M University Press. 2019. Retrieved May 9, 2021.
- Dansby, Andrew. "Folklorist Mack McCormick dies - Houston Chronicle". Chron.com. Retrieved November 26, 2015.