In 1632, he joined the great Puritan exodus and sailed from England to the Massachusetts Bay Colony, settling in Dorchester where he was promptly appointed as the captain of the local militia. In 1633, he commanded the first American naval task force and pursued the pirate Dixie Bull, routing him from New England waters. He and Roger Ludlow planned and supervised the construction of the first fortifications on Castle Island (later known as Fort Independence) in Boston Harbor. In 1634, he was elected to represent Dorchester in the Massachusetts General Court, where permission was granted for him to remove to the fertile Connecticut River valley. In 1635, he settled in Windsor, Connecticut at the confluence of the Farmington River and the Connecticut River; he lived there for the next twelve years and served as a civil Magistrate and military leader of the nascent Connecticut Colony. In 1640, he married Anne Peck from a prominent Puritan family; they had eight children.
The most prominent episode in Mason's lifelong career of public service was his overall command as captain of the Colonial forces in the Pequot War in 1637. This was the first declared and sustained conflict in Southern New England, a complex and risky campaign. The large and powerful Pequot Tribe had antagonized other local tribes and had killed several Colonial settlers. The Massachusetts Bay Colony eventually declared war with them, and Connecticut Colony was quickly drawn into the conflict.
