Leonidas Dyer was born in Warren Country, Missouri, on 11th June, 1871. After attending Central Wesleyan College and Washington University he was admitted to the bar in 1893. He practiced law in St. Louis, Missouri before serving in the Spanish-American War.

Dyer, a member of the Republican Party, was elected to Congress in 1911. He was defeated in 1914 but returned to Congress in 1915. A strong opponent of racial intolerance, Dyer made several unsuccessful attempts to persuade Congress to pass a federal anti-lynching law.

After eighteen years in Congress Dyer was defeated in 1933. Two attempts to return to Congress in 1934 and 1936 ended in failure. Leonidas Dyer, who returned to his law practice, died in St. Louis on 15th December, 1957.