He served as secretary of the U.S. legation when Martin Van Buren was US Minister to Britain in 1831 and 1832, after which he practiced law in Albany, New York.

Van Buren later practiced law in New York City, where he developed a reputation as an effective trial attorney, with his memory for details and oratorical skills making him a formidable courtroom advocate.

In 1848, Van Buren led the Barnburners—New York Democrats opposed to the election of Lewis Cass as president on the grounds that he was too friendly to the slaveholding South.

In Van Buren's later years he traveled extensively; he died aboard ship while en route from England to New York, and was buried at Albany Rural Cemetery.

[5] Contemporaries said he had a remarkable memory and that "his success at the bar was great, but his fame as a lawyer has been dimmed by his wit and his wonderful ability as a politician.

[10] In 1845, he conducted the prosecution of some leaders of the Anti-Rent War at their trial for riot, conspiracy and robbery in protest of attempts by the wealthy owners of Van Rennsselaer Manor and other large upstate New York land grants to collect overdue rents, which Stephen Van Rensselaer and other patroons had long deferred.

[11] At the re-trial, in September 1845, the two leading counsel started a fist-fight in open court, and were both sentenced by the presiding judge, Justice John W. Edmonds, to solitary confinement in the county jail for 24 hours.

[11] Governor Silas Wright refused to accept Van Buren's resignation, and both counsel continued with the case after their release from jail.

[10] In December 1845, Governor Wright charged Van Buren to work on an act to limit the tenure of the manor lords.

[12] As a result, the landlords subdivided their large manor holdings for sale to individual farmers and homeowners or commercially developed them.

[13] The defense, led by William H. Seward, tried to prove that Freeman was insane and therefore could not stand trial, but a jury empaneled to consider the question disagreed, siding with Van Buren.

[17] The Barnburners met for a State Convention in Utica, New York on June 22 and nominated Martin Van Buren as their presidential candidate.

[19] Though most former Free Soil members became Republicans because of the slavery issue, many including Martin and John Van Buren chose to return to the Democratic fold.

"[6] On October 13, 1866, Van Buren died from kidney disease while at sea near Cape Race, Newfoundland as he traveled from Liverpool to New York City aboard the steamship Scotia.