On July 4, 1776, Ewing was commissioned a brigadier general in the Pennsylvania militia. Characterized by historian David Hackett Fischer as a "hard-driving Scotch-Irish border chieftain", Ewing commanded a brigade of five regiments at the time of George Washington's crossing of the Delaware River on the night of December 25–26, 1776, in a surprise attack on the Hessian forces in Trenton, New Jersey. Ewing's force, positioned directly across from Trenton, was unable to cross the river because of the ice. Although Ewing has sometimes been criticized by historians for failing to join Washington on the other side of the river, Fischer argues that no one could have crossed the river at that point that night. Washington did not blame General Ewing, writing that "the Quantity of Ice was so great, that tho' he did every thing in his power to effect it, he could not get over."