A member of the political Conway-Johnson family that dominated the state and national delegations in the antebellum years, he was elected by the legislature as a Democratic U.S.

He was elected as a Jacksonian Delegate to the 20th US Congress to fill the vacancy caused by the death of Henry Wharton Conway, killed as a result of a duel with a former friend.

During the 29th Congress, he was allowed to hold the seat of President pro tem of the Senate for a day, though he was not elected to that post.

In 1848 Sevier and Nathan Clifford, the Attorney General of the United States, were appointed ambassadors to Mexico by President James K. Polk to negotiate the Treaty of Guadalupe Hidalgo at the end of the Mexican–American War.

After completing this project, Ambrose Hundley Sevier died the last day of that year on his plantation in Pulaski County, Arkansas.