Andrus went to school in Danbury, Connecticut. After finishing school, he returned to Malone and initially worked as a clerk in Jonathan Stearns' store. He soon left the job and worked for Jonathan Thompson, driving a mail coach between Plattsburgh and Ogdensburg until 1832. In 1842, he became a proprietor of that mail route, which he maintained until it was superseded by the railroad in 1851. When the Bank of Malone was founded in 1851, he became one of its directors, a position he was annually re-elected to. He was the only surviving member of the original board when he died.[3] He also worked as a farmer and sold village lots from large tracts of land his father owned.[2]
In 1832, Andrus married Susan Roberts of Chateangay.[3] They had three surviving sons. He was a member and senior warden of St. Mark's Episcopal Church.[6]