Born in Indiana, Pennsylvania, he attended the public schools and graduated from Jefferson College, Canonsburg, Pennsylvania. He studied law and was admitted to the bar in 1845.
He began practicing in Hollidaysburg, Pennsylvania in 1846. Blair was a delegate to the 1856 Republican National Convention, and was elected to the House of Representatives as a Republican in 1858 and 1860. During the Thirty-seventh Congress, Blair was chairman of the United States House Committee on Private Lands.
He unsuccessfully ran for reelection in 1862 and resumed the practice of law.
He was again an unsuccessful candidate for election to Congress in 1874.
Member United States House