When United States Senator Charles Sumner died in March 1874, the state senate, which then chose the state's US senators, met to choose his replacement. After a long and contentious debate involving thirty-three ballots, Washburn was chosen to succeed Sumner as a compromise candidate acceptable to supporters of Henry L. Dawes and George F. Hoar. Washburn then resigned the governorship, leaving Lieutenant Governor Thomas Talbot as Acting Governor. Washburn served from April 17, 1874 until the term ended on March 3, 1875, and refused to run for reelection.