General Agnew was engaged at the Battle of Long Island in 1776. In 1777, Agnew accompanied British forces under the command of General William Tryon and General William Erskine on an inland raid against Patriot supply depot in Danbury, Connecticut. After successfully destroying Patriot supplies, the British forces engaged and defeated Continental Army Generals David Wooster, Benedict Arnold, and Gold S. Silliman and Patriot militiamen in the Battle of Ridgefield. Lastly, Agnew was at the Battle of the Brandywine, where he was wounded.