Joseph Mansfield was born in Wayne, Texas, on 9th February, 1861. After attending local schools he became a farm labourer in Alleyton. Later he worked as a baggage-master and freight clerk with the Southern Pacific Railway.
Mansfield studied law and was admitted to the bar in 1886 and became a lawyer in Eagle Lake. He also established a local newspaper in the town. Mansfield became mayor of Eagle Lake in 1889. He was also prosecuting attorney of Colorado County (1892-1896) and judge of Colorado County (1896-1916).
A member of the Democratic Party Mansfield was elected to Congress in 1917. He served as chairman of the Committee on Rivers and Harbors (72nd through to 79th Congress).
Joseph Mansfield died on 12th July, 1947.