Green was a delegate to the
State constitutional convention in 1845 and was elected as a Democrat to the
30th and
31st Congresses, serving from March 4, 1847, to March 3, 1851. He was not a candidate for renomination in
1850, and was subsequently
Chargé d'Affaires to New Granada in 1853–1854. He was appointed
Minister Resident in June 1854, but did not present his credentials; he was elected to the
35th Congress, but did not take his seat, having been elected to the U.S. Senate to fill a vacancy during the term commencing March 4, 1855, where he served from January 12, 1857, to March 3, 1861. While in the Senate, he was chairman of the Committee on Territories during the
35th and
36th Congresses. ==Death==