He transferred to the 17th Foot on 26 October 1775[a] and served with this regiment during General Howe's early campaigns of the American War of Independence.

Despite some early success in checking the American advance and the killing of his opposite, the highly popular Hugh Mercer; Mawhood's post was overrun and the battle was lost after Washington brought forward reinforcements.

He broke through Washington's attempted encirclement by leading a bayonet charge across a bridge, in doing so he managed to escape with most of his force, averting an ignominious fate like that suffered by Colonel Rall the week prior in similar circumstances.

[4] Mawhood continued to serve in North America, seeing further action during the 1777–1778 Philadelphia campaign leading a mixed force of regulars, loyalists and rangers in a series of raids through New Jersey.

In 1780 Mawhood was chosen to lead reinforcements to the besieged garrison, arriving with the fleet of Admiral George Rodney which broke through the French blockade in January.