 Born in 1753 into an upper-class family of New York City, Abraham was the great-grandson and namesake of former city mayor Abraham de Peyster.Upon the outbreak of war in 1775-1776 between the rebel colonists and the colonists loyal to King George III, de Peyster chose the King's side.He served in the King's American Regiment, a regiment of Loyalists who were ordered to serve in the interior of the American colonies to re-awaken loyal sentiment and hearten those opposed to the rebels, and was commissioned in December 1776 as a captain.