In 1776, Gist was appointed major of Smallwood's Maryland Regiment, and was with them in the Battle of Long Island, where they fought a delaying action at the Old Stone House (Brooklyn, New York), allowing the American army to escape encirclement. In January 1779, the Continental Congress appointed him as a brigadier general in the Continental Army, and he took the command of the 2nd Maryland Brigade. He fought stubbornly at the Battle of Camden in South Carolina in 1780. He joined the southern army under Nathanael Greene, and he was given the command of the light corps again when the army was remodeled in 1782. On August 26, 1782, he rallied the broken forces of the Americans under John Laurens after they had been scattered in an ambush set by a British foraging party. At one time after a bayonet charge, his force secured fifty prisoners, but the British under Lord Cornwallis rallied, and the Marylanders gave way. Gist escaped, and, a year later, he was present at the surrender of Cornwallis at Yorktown. He was admitted as an original member of The Society of the Cincinnati of Maryland and was elected as the first vice president of the Maryland Society on November 22, 1783. Mordecai Gist died in 1792, in Charleston, South Carolina.