Sherman was in Portsmouth by May 1638 when he was present at a general meeting, and the following year, he was selected as Secretary. In 1640, he and four others were chosen to lay out lands within the town, and the following year, he was made a freeman. From 1648 to 1651, he was the General Recorder for the town, and from 1649 to 1656, he was the town clerk. He sat on the Portsmouth town council for many years from 1649 to 1657, and again in the early 1670s, but appears to have stayed out of public service between 1657 and 1665. From 1665 to 1667, he once again served in a civil capacity when he was elected as a Deputy from Portsmouth.