Greene helped organize a militia unit, the Kentish Guards, in 1774. Because of his limp he was deemed unfit to be an officer. Instead he marched as a private for eight months until it became obvious that with man of his talents the limp could be forgotten. In May of 1775 the Rhode Island Assembly authorized the formation of a 1,500 soldiers and Greene was named commander. This force joined with the rest of Washington's forces surrounding Boston. With the British evacuation of Boston in March 1776, Washington placed Greene in command of the city before dispatching him south to Long Island.
Greene was promoted to Major General in August 1776 and put in charge of the Revolutionary army on Long Island. After constructing fortifications during early August, he missed the Battle of Long Island on the 27th due to a severe fever. He commanded troops at the Battle of Harlem Heights. He was moved to command of Ft. Washington(on Manhattan) and recommended that the fort be defended. This fort and Ft. lee across the river were taken by the British and Greene was blamed for the defeat.
Washington did not lose confidence in his general. He led troops in the Battles of Trenton in New Jersey and Brandywine and Germantown in Pennsylvania, and acted as quartermaster general at Valley Forge, Pennsylvania. While serving as quartermaster he also led operations in the field at Monmouth and in Rhode Island. Greene replaced Benedict Arnold as the commander at West Point in early 1780. He also headed the board of general officers that condemned John Andre' to death.