Metcalf won the 1855 race for Governor, defeating incumbent Nathaniel B. Baker, James Bell and Asa Fowler. In 1856 he defeated John S. Wells and Ichabod Goodwin, but his margin over Wells was narrow, and the selection moved to the New Hampshire General Court, which chose Metcalf. Metcalf became identified with the Republican Party when it was founded as the major anti-slavery party in the mid 1850s. In addition to his abolitionist views, Metcalf's governorship was noteworthy for his support of a prohibition law, which passed in 1855, and remained in force until 1889.