William Pitt Fessenden (born October 16, 1806) was a United States senator from the state of Maine and a member of the Republican Party. A male legislator who would become one of Maine’s long-serving federal representatives, he entered the Senate on May 31, 1841. His service in the chamber extended through December 31, 1869, marking a lengthy national career that spanned much of the mid-nineteenth century.

Fessenden represented Maine in the United States Senate for four terms, holding office continuously from 1841 to 1869. During this period, he served as a senator rather than a member of the House, and he did not represent a specific numbered district, as senators serve their entire state. His long tenure placed him among the more enduring figures in Maine’s congressional delegation of his era.

By the time his Senate service concluded on December 31, 1869, William Pitt Fessenden had spent nearly three decades in national office. Identified in congressional records by the bioguide ID F000099, he is remembered as a historical member of Congress from Maine whose career was closely tied to the rise and consolidation of the Republican Party in the United States.