Dr. Southgate was a physician, lawyer, judge, gentleman farmer and a business man. His interest were many and varied. He gave up being a physician after becoming interested in law and being appointed judge of the Court of Common Pleas.

He also initiated one of the first diking experiments in Maine to increase salt marsh hay production. He headed the Scarborough Turnpike Corporation along with William and Cyrus King. This company built the Cumberland Turnpike which was a toll road across the marsh between Dunstan and Oak Hill.