Born in Dublin in 1623, Downing spent his childhood in London before emigrating to New England with his family as part of the Puritan migration. (John Winthrop, the founding governor of the Massachusetts Bay Colony, was his uncle.) A member of Harvard’s first graduating class in 1642, Downing initially served as a preacher aboard a Caribbean trading vessel. Returning to England, where Royalists and Parliamentarians were at war, Downing was appointed chaplain to Col. John Okey’s regiment in Parliament’s New Model Army. Later he served as chaplain and secretary to Arthur Hesilrige, a member of parliament and a close friend of Downing’s father. Downing’s abilities would catch Oliver Cromwell’s attention, leading to his appointment as scoutmaster general—the head of Parliament’s intelligence operations.