Gainer is a surname. Notable people with the name include:
Aaron Gainer, member of American Christian post-grunge band '12 Stones' Alice Gainer (born 1982), American television reporter Amari Gainer (born 2000), American football player Del Gainer (1886–1947), American baseball player Derrick Gainer (American football) (born 1966), American football player Derrick Gainer (born 1972), American boxer Sir Donald Gainer (1891–1966), British ambassador Elmer Gainer (1918–1970), American basketball player Forrest Gainer (born 1979), Canadian rugby player Frank Gainer (1888–1975), Canadian politician Glen Gainer Jr. (1927–2009), American politician Glen Gainer III (born 1960), American politician Jay Gainer (born 1966), American baseball player John L. Gainer (born 1938), American chemical engineer Ronald William Gainer (born 1947), American Catholic priest, appointed Bishop of Harrisburg in 2014 Steve Gainer (born 1962), American cinematographer Terrance Gainer (born 1947), Sergeant at Arms of the United States Senate 2007–14