Initially a member of the Democratic-Republican Party and later a Democrat, he was elected to the Vermont House of Representatives in 1818. He served as Chief Justice of the Supreme Court of Vermont from 1821 to 1823. In 1823 he became Governor of Vermont. After being twice re-elected, in 1826 he declined re-election and went back to practicing law until 1829 when he became envoy extraordinary and minister plenipotentiary to the court of Spain. William T. Barry was appointed to the post in April, 1835, but died in Liverpool on August 30, without assuming his duties in Spain. President Jackson then appointed John H. Eaton, and Van Ness departed on December 21, 1836.