During the colonial militia buildup at the onset of the American Revolution, on 12 Sep 1775, Buckner was elected lieutenant colonel of the minutemen raised by the combined Virginia counties of Spottsylvania, Caroline, Stafford, and King George under Col. Hugh Mercer. Both Buckner and Mercer were members of the Spottsylvania County committee. Having served under George Washington during the earlier war, he was not long after appointed commander of the 6th Virginia Regiment in the nascent Continental Army. His colonel's commission dated from 13 February 1776. The two other field officers were Lieutenant Colonel Thomas Elliott and Major James Hendricks. The regiment came into existence on 28 December 1775. It was organized at Williamsburg, Virginia in the strength of ten companies from men of ten different eastern and southern counties. Initially assigned to the Southern Department, the unit transferred to Stephen's Brigade in Washington's main army on 3 September 1776. Buckner commanded the 191-strong 6th Virginia at the Battle of Trenton on 26 December 1776. At that time, Hendricks was lieutenant colonel and Richard Parker was major. For reasons not given, Parker led the regiment at the battles of Assunpink Creek and Princeton on 2 and 3 January 1777.