Sergeant was born on December 2, 1881 in Mansfield, Texas to Gustavis A. Sergeant and Harriet (Hattie) P. Baldwin. He married Mary Marshall Brown, daughter of Doctor Horace M. Brown and Mary Elizabeth Rudd, on 25 August 1909 in Union, Monroe County, West Virginia.
They had two children. Their first child, Mary Marshall Sergeant, died in infancy. He attended school in Dallas and graduated from the University of Texas where he also received his law degree.
In 1908 he began private practice in Dallas, but was soon appointed city judge.
He served in a number of political positions. He was mayor during the time of the Texas Centennial celebration held at Fair Park in Dallas, and has been referred to as "The Centennial Mayor.
Sergeant died August 26, 1971 in Dallas, Texas and was interred at the Oak Cliff Cemetery, Dallas.
