Born in Philadelphia to Irish immigrant parents, William and Elizabeth Magaw, Robert Magaw rose to prominence as a lawyer in Carlisle, Pennsylvania. Magaw had served in the militia several years prevously, but caught revolutionary fervor, and Magaw was commissioned as a Colonel in the Continental Army. He was put in command of the 5th Pennsylvania Battalion and was commander of the American garrison at Fort Washington during the New York campaign. There, he was forced to surrender and became a prisoner of war on November 16, 1776. While he was set at liberty in New York City, his parole dictated that he could not leave the city until he was exchanged. While on parole Magaw met and married Marritie Van Brunt. He was exchanged October of 1780 and proceeded to return home to Carlisle. He resumed his work as a lawyer and later served in Pennsylvania’s House of Representatives from 1781-82.