Previously Key had been the Assistant Surgeon General and director of the Bureau of Occupational Safety and Health.

[3] In 1974, B.F. Goodrich Chemical Company contacted NIOSH concerning deaths and illnesses in its Louisville factory.

His published recommendation suggested that vinyl chloride used in the factory resulted in four fatalities from angiosarcoma of liver.

In 1985, he was contacted by Labor Secretary Bill Brock about heading the Occupational Safety and Health Administration (OSHA).

[8][9] In September 2013 Shell Oil Company partnered with the University of Texas School of Public Health to endow the Marcus M. Key, M.D.-Shell Occupational and Environmental Health Endowed Chair in honor of Key to provide funding to recruit and retain senior faculty in the school’s Occupational Medicine Program of the Division of Epidemiology, Human Genetics and Environmental Science.