Born near Asheboro, North Carolina, Hammer attended private and common schools.

He was admitted to the bar in September 1891 and commenced practice in Asheboro, North Carolina.

He served as mayor of Asheboro, member of the city council, school commissioner (1895–1899), and local Superintendent of public instruction (1891–1895 and again in 1899-1901).

He was appointed United States attorney for the Western District of North Carolina on February 24, 1914, and served until September 20, 1920.

Hammer was elected as a Democrat to the Sixty-seventh and to the four succeeding Congresses and served from March 4, 1921, until his death in Asheboro, North Carolina, September 26, 1930.