Root graduated from Dartmouth College in 1793 and became a teacher. Then he studied law, was admitted to the bar in 1796, and commenced practice in Delhi, New York. He was a member of the New York State Assembly (Delaware Co.) in 1798–99, 1800–01 and 1802. Root was elected as a Democratic-Republican to the 8th United States Congress, holding office from March 4, 1803, to March 3, 1805. Afterwards he resumed his law practice. He was then elected to the 11th United States Congress, holding office from March 4, 1809, to March 3, 1811, and was Chairman of the Committee on Claims. Root was a member of the New York State Senate (Middle D.) from 1812 to 1815, sitting in the 35th, 36th, 37th and 38th New York State Legislatures.
In 1815, Root contested successfully the election of John Adams to the 14th United States Congress, and took his seat on December 26, 1815, served until March 3, 1817, and was Chairman of the Committee on Expenditures in the War Department.
He was again a member of the State Assembly (Delaware Co.) in 1818, 1819, 1820 and 1820–21; and was a delegate to the New York State Constitutional Convention of 1821. He was Lieutenant Governor of New York from 1823 to 1824, but was defeated when running for re-election on the ticket with Samuel Young in 1824. He was again a member of the State Assembly (Delaware Co.) in 1826, 1827, 1828 and 1830; and was Speaker in 1827, 1828 and 1830. He was elected as a Jacksonian to the 22nd United States Congress, holding office from March 4, 1831, to March 3, 1833, and was Chairman of the Committee on Agriculture. In 1838, this time as a Whig, he ran again for the House but was defeated. He was again a member of the State Senate (3rd D.) from 1840 to 1843, sitting in the 63rd, 64th, 65th and 66th New York State Legislatures.
Root also served as Major-General of the New York State Militia.
He was originally buried at the Old Cemetery, but later re-interred at Woodland Cemetery, both in Delhi NY.
-  Political Graveyard
- Erastus Root at the Biographical Directory of the United States Congress
- John Stilwell Jenkins: History of Political Parties in the State of New-York (Alden & Markham, Auburn NY, 1846)
-  Bio at Virtual American Biographies