 From 1655 to 1656 he was commissioner for security and in 1657 he was commissioner for assessment for Suffolk and Bury 1657.In 1659, Chaplin was commissioner for militia for Suffolk and was elected Member of Parliament for Bury St Edmunds in the Third Protectorate Parliament.He was commissioner for assessment for Suffolk in January 1660 and commissioner for militia for Bury in March 1660.