He attended Yale College from 1779 to 1782, and graduated from Harvard University in 1783. He studied law with John Canfield (ca.1740-1786) at Sharon, Connecticut, with John Bay at Claverack, New York, and with Ezekiel Gilbert at Hudson, New York. He married John Canfield's daughter Laura (1768–1807) in 1784. He was admitted to the bar and commenced practice in Hudson, N.Y., where he was city clerk from 1786 to 1793.
From 1796 to 1801, he was Assistant Attorney General for the Third District, comprising Columbia and Rensselaer counties. He was New York Attorney General from 1802 to 1804. From 1804 to 1819, he was an associate justice of the New York Supreme Court, and Chief Justice from 1819 until the end of 1822. He was legislated out of office by the State Constitution of 1821. Governor Joseph C. Yates nominated him to be re-appointed, but this was rejected by Bucktails majority in the State Senate, Spencer having been the longtime leader of the Clintonians.
In 1825, he was the Clintonian candidate for U.S. Senator from New York, and received a majority in the State Assembly. The Bucktails majority in the State Senate did not nominate any candidate, thus preventing Spencer's election on joint ballot. The seat remained vacant until the election of Nathan Sanford in 1826. Afterwards Spencer resumed the practice of law in Albany.
He was elected to the 21st United States Congress, serving from March 4, 1829, to March 3, 1831; during this Congress, he was a member of the Committee on Agriculture. He was one of the managers appointed by the House of Representatives in 1830 to conduct the impeachment proceedings against Judge James H. Peck of the U.S. District Court for the District of Missouri.
After the death of Ambrose's first wife Laura Canfield (1768–1807), he married Mary Clinton (1773–1808, sister of Governor DeWitt Clinton). After Mary's death, he married her sister Katherine Clinton (1778–1837).
U.S Representative James B. Spencer was a distant cousin of him.
- Ambrose Spencer at the Biographical Directory of the United States Congress
- Clinton genealogy
- Clinton genealogy, at rootsweb
- List of NY State Attorneys General, at Office of the Att. Gal. of NY
- The American Almanac and Repository of Useful Knowledge for the Year 1849 (page 338, Charles C. Little & James Brown, Boston, 1848)
- Canfield genealogy
Josiah Ogden Hoffman
|New York Attorney General
Stephen Van Rensselaer
|United States House of Representatives
1829 - 1831