On 13 August 1776, Parker became a major in the 6th Virginia Regiment. This regiment was transferred to Adam Stephen's brigade in George Washington's main army on 3 September 1776. The 6th Virginia, only 191 men strong, under Colonel Mordecai Buckner is noted in the order of battle for the Battle of Trenton on 26 December 1776. Major Parker is listed as acting commander of the 6th Virginia at the time of the battles of Assunpink Creek and Princeton on 2 and 3 January 1777.