Blair was elected as a Jacksonian Republican to the Eighteenth Congress and re-elected as a Jacksonian to the Nineteenth through Twenty-third Congresses. He served as a U.S. Representative from March 4, 1823 to March 3, 1835. During the Twentieth Congress, he was chairman of the U.S. House Committee on Expenditures in the State Department. He was chairman of the Committee on Expenditures in the Department of State (Twentieth Congress). He was an unsuccessful candidate for re-election to the Twenty-fourth Congress in 1834.