In 1630 Robert, Mary and Nathaniel sailed with John Winthrop as a part of the original Puritan expedition to Massachusetts. Soon after arriving in the New World, Seeley became one of the original forty settlers of Watertown, one of Massachusetts' earliest Puritan communities. He employed his training in surveying by laying out many of the plots for the settlers. He was granted freeman status in 1631.
In 1633 or 1634, Seeley joined a ten-man expedition led by John Oldham to the Connecticut River. The group soon established Wethersfield, the first English settlement on the Connecticut River. Oldham's death in 1636, presumed by the colonists to be at the hands of the Pequot, helped touch off the Pequot War in 1637. Seeley served as second-in-command to Captain John Mason in the war. He was severely wounded by an arrow to the head in an attack on a Pequot fort along the Mystic River. Captain Mason, who called Seeley a "valiant soldier", wrote of the incident, "Lieutenant Seeley was shot in the eyebrow with a flat headed Arrow, the Point turning downwards. I pulled out the arrow myself." Seeley carried a permanent scar from the wound.
New Haven
When his old friend John Davenport arrived in Massachusetts, Seeley joined his group and helped establish the New Haven Colony in 1638. Seeley served as New Haven's first town marshal and lieutenant of the militia. He was generally known in the community as Lieutenant Seeley. He also participated in Theophilus Eaton's exploratory expedition in Long Island Sound.
Later life
In 1659 Seeley briefly returned to England, living there until 1662 when he returned to the New World and settled in New Amsterdam on Long Island. He died in New York City in 1668. In 1695 his heirs received of land in Watertown, resolving a suit which Seeley had filed 60 years earlier after settling in Wethersfield. In the suit he had claimed that he had not been given the area promised to the original settlers of Watertown. Seeley's son Nathaniel was killed in the build-up to the Great Swamp Fight during King Philip's War.
Honors
Robert Seeley's name is featured on three historic plaques listing town founders, in Watertown, Wethersfield, and New Haven.
He is listed on a historic plaque at the base of a statue honoring John Mason as one who helped achieve victory for the colonists over the Pequot.