Emery taught at Phillips Exeter for a year in 1797, with Daniel Webster being one of his students, before beginning his legal practice in Parsonsfield, Maine. In 1807, he moved to Portland. In 1816, Emery attended the Brunswick Convention that voted to separate the state of Maine from Massachusetts; three years later he would serve as a delegate to the 1819 Maine Constitutional Convention for Cumberland County, though he did not sign the constitution. He represented Portland in the newly created Maine House of Representatives for three years starting in 1820.
