In 1776, Colonel John Cadwalader was elected senior officer of the Philadelphia Associators, a volunteer militia founded by Benjamin Franklin in 1747. By December, Cadwalader and the Associators were positioned about 10 miles south of Trenton on the west side of the Delaware River in Bucks County, Pennsylvania at the ferry between Bristol, Pennsylvania and Burlington, New Jersey. Cadwalader had received orders to send his column across the river on the night of December 25–26 and march to Trenton from the south.

Meanwhile, George Washington's column would cross the river to the north of Trenton and attack the city from that direction. After successfully crossing his light forces, Cadwalader discovered that river ice prevented crossing his artillery. He then returned his column to the Pennsylvania side, leaving Washington's forces unsupported in New Jersey. It was fortunate for Washington that a Hessian column, having marched from their garrison at Bordentown to Mount Hollywhere they were engaged in the Battle of Iron Works Hill, were no longer in position to defend Trenton. Washington was successful in his surprise attack on the morning of December 26 against the Hessian garrison in Trenton.

Cadwalader and his column did cross the river the next day. Cadwalader subsequently took part in the further actions in New Jersey, which forced the British commander General William Howe and his principal subordinate, Lord Cornwallis, to surrender the colony to the Americans.

After the Conway Cabal, he fought a duel with Thomas Conway in 1778 in which Cadwalader wounded his opponent with a shot in the mouth. Supposedly Cadawalader, a supporter of Washington throughout the cabal, boasted, "I have stopped that damned rascal's lying anyway" as he stood over the bleeding Conway.