Jacob Collamer was born in Troy, New York. He graduated from the University of Vermont in 1810, studied the law, and then served as a lieutenant of artillery in the Vermont militia during the War of 1812.

Following the war, Collamer was admitted to the Vermont state bar in 1813 and practiced the law while also serving in Vermont state politics. He served in the state house of representatives, worked as the state's attorney for Windsor County from 1822 to 1824, and then served as judge on the state superior court from 1833 to 1842. A Whig, Collamer was elected to the United States House of Representatives in 1842, and served in that body from 1843 to 1849.

Collamer was tapped by President Zachary Taylor to serve as postmaster general, a position he held from 1849 until he resigned in 1850 following President Taylor's death. Following this stint, Collamer returned to Vermont and reclaimed his position of judge on the state superior court, a position he held from 1850 to 1854. Jacob Collamer was elected to the United States Senate as an antislavery Republican in 1855 and served in the Senate until his death in 1865.