| William T. Haines | |
| Order1: | 49th |
| Office1: | Governor of Maine |
| Term Start1: | January 1, 1913 |
| Term End1: | January 6, 1915 |
| Predecessor1: | Frederick W. Plaisted |
| Successor1: | Oakley C. Curtis |
| Office2: | Maine Attorney General |
| Term Start2: | 1897 |
| Term End2: | 1900 |
| Governor2: | Llewellyn Powers |
| Preceded2: | Frederick A. Powers |
| Succeeded2: | George M. Seiders |
| Office3: | Member of the Maine Senate |
| Term3: | 1888-1892 |
| Birth Name: | William Thomas Haines |
| Birth Date: | 7 August 1854 |
| Birth Place: | Levant, Maine |
| Death Place: | Augusta, Maine |
| Party: | Republican |
| Alma Mater: | University of Maine Albany Law School |
William Thomas Haines (August 7, 1854 - June 4, 1919) was an American politician and the 49th Governor of Maine.
William Thomas Haines was born in Levant, Maine on August 7, 1854. As an undergraduate at the University of Maine, he founded the Eternal Companions Society[1] on the Orono Campus in 1875. The fraternity was later chartered as the Beta Eta chapter of Beta Theta Pi[2] and Haines was issued roll number 1 in the new organization. He graduated as Valedictorian[3] of the University of Maine class of 1876 and went on to study law at Albany Law School where he completed his LL.B. degree in 1878. In May, 1879, Haines settled at Oakland (then West Waterville), Kennebec County, Maine, and commenced the practice of law. He remained there until October, 1880. He then moved to Waterville, Maine.
Haines became the county attorney of Kennebec County in 1882. He held that position for five years. He became a member of the Maine State Senate in 1888. He held that position until 1892. He became a member of the Maine House of Representatives in 1895. He served as the attorney general of Maine (1896-1901) and then became a member of the governor’s executive council (1901-1905).
Haines was nominated for the governorship of Maine by the Republican Party in 1912. He went on to win the general election by a popular vote. He held the governor's office from January 1, 1913 to January 6, 1915. During his administration, a bond issue was authorized for road improvements. A public utilities bill and an anti-trust act were sanctioned. He was unsuccessful in his re-election bid.
Haines married Edith S. Hemenway. He had three children. He was a Unitarian.