Wyndham Mortimer (March 11, 1884 – August 25, 1966) was an American trade union organizer and functionary active in the United Auto Workers union (UAW). Mortimer is best remembered as a key union organizer in the 1937 Flint Sit-Down Strike. Mortimer was the First Vice President of the UAW from 1936 to 1939. A member of the Communist Party USA from about 1932, Mortimer was a critic of the efforts of the conservative American Federation of Labor to control the union and was a leader of a so-called "Unity Caucus" which led the UAW to join forces with the more aggressive Congress of Industrial Organizations (CIO).
In the spring of 1941, Mortimer's refusal to follow the anti-strike line of the UAW's governing Executive Board during a highly controversial work stoppage at a California aircraft factory lead to his termination by the union and effectively brought an end to his career.
Wyndham Mortimer was born March 11, 1884 in Karthaus, Pennsylvania, the son of a coal miner who was a member of the Knights of Labor, an early American labor union. He later recalled that one of his earliest memories of life as a young boy in Central Pennsylvania involved "walking behind parades of striking miners."
Mortimer left school at age 12 to work in the mines of Pennsylvania as a coal trapper, periodically operating trap doors in the mine shafts to allow the passage of carts and to assist with ventilation. Mortimer joined the United Mine Workers of America in 1900 and remained in the mines for several years after that date.
Mortimer joined the Socialist Party of America in 1908 after hearing a campaign speech by that party's Presidential nominee, Eugene V. Debs.