Then he studied law in the office of Van Buren & Butler, was admitted to the bar, and practiced in Albany.
On September 2, 1845, he married Margaret Crane Alling (1812–1900), a sister of his first wife, and their son was Verplanck Colvin (1847–1920), the ideator of the New York Forest Preserve.
Andrew J. Colvin was District Attorney of Albany County from 1846 to 1847, and from 1851 to 1853; and a member of the New York State Senate (13th D.) in 1860 and 1861.
He was buried at the Grove Cemetery in Coeymans.
Assemblyman John Colvin (1752–1814) was his grandfather.