Robertson was elected as a Democratic-Republican to the Fifteenth, Sixteenth, and Seventeenth Congresses and served from March 4, 1817, until his resignation in 1821, before the convening of the Seventeenth Congress. He served as chairman of the Committee on Private Land Claims (Fifteenth Congress). He served as member of the Kentucky House of Representatives 1822-1827, serving four years as speaker. He declined the appointment as Governor of Arkansas Territory tendered by President James Monroe and the diplomatic posts of United States Minister to Colombia in 1824 and to Peru in 1828. He served as Secretary of State of Kentucky in 1828. He was appointed associate justice of the Kentucky Court of Appeals in 1829 and served as chief justice from 1829 to 1834, when he resigned. He resumed the practice of law in Lexington, Kentucky, and became professor of law in Transylvania University 1834-1857.
