Warren, the son of James Rainey and Fannie Ann Leak Warren, grew up in Montgomery and attended the Starke University School there. He completed a bachelor of science in engineering at the Alabama Polytechnic Institute in Auburn in 1897, then went on to study architecture under William R. Ware at Columbia University in New York, New York. After graduating in 1902 he worked in the offices of McKim, Meade and White for four years, then spent a year in Philadelphia, Pennsylvania with Albro & Lindeberg before returning to Alabama.
In 1907 Warren partnered with fellow McKim, Meade & White alumnus William Welton in Birmingham. Before moving to Birmingham in 1907, Warren & Welton had already solicited for work in the rapidly-growing city. They published an unbuilt proposal for Southside Baptist Church in 1908. Their physical move south was probably made possible by the commission for the 16-story Empire Building, a design originally conceived by J. E. R. Carpenter of the New York firm of Carpenter and Blair, but carried out with the younger architects on-site. They opened their own office in the building after it was completed in 1909 and began receiving other commissions, such as the Boy's Industrial School and Chamber of Commerce Building, along with several residences and interiors.
The partnership split in 1910, with Warren finding Welton's aggressiveness in marketing his services to be unpalatable. He practiced independently for several years before accepting an invitation from Eugene Knight which resulted in the firm of Warren & Knight, which became Warren, Knight & Davis with the addition of John Davis in 1922. Through that firm's long tenure as the preeminent practitioners in Birmingham, Warren specialized in the design of details. In an address to the Civitan Club in 1928, Warren expressed the view that American architectural practice had surpassed Europe, particularly with regard to the demands and constraints of modern infrastructure and real estate financing. Warren was made a fellow of the American Institute of Architects in 1934.
Warren married the former Dorothea Orr, granddaughter of John T. Milner on December 18, 1912. They had two children, Dorothy and William Jr. Their residence was at 1445 Milner Street in Highland Park.
- Owen, Thomas McAdory and Marie Bankhead Owen (1921) History of Alabama and Dictionary of Alabama Biography. 4 volumes. Chicago, Illinois: S. J. Clarke Publishing Co.
- "Whittlings" (March 1928) Pencil Points, p. 198
- 1956 American Architects Directory (December 1955) American Institute of Architects/ R. R. Bowker
- William T. Warren Papers at bplonline.com