The son of Supreme Court Associate Justice Thomas Todd, he was born near Danville, Kentucky, and graduated from the College of William and Mary in 1809. He was a subaltern and judge-advocate of General James Winchester's division in the War of 1812. In 1813, he was made a captain of infantry, and was an aide to General William Henry Harrison in the Battle of the Thames. In March, 1815, he was made Aide-de-Camp to Governor Isaac Shelby, with the rank of colonel.
In 1817, he was appointed Secretary of State of Kentucky. In 1820, Todd was appointed a Confidential Agent to Gran Colombia, where he would remain until 1824. From 1841 to 1846 he served as the fifteenth United States Ambassador to Russia. He died in Baton Rouge, Louisiana, and was buried at Rosehill Elmwood Cemetery
Todd married Isaac Shelby's youngest daughter, Letitia, on June 15, 1816. They had twelve children.