[2][3] While in Boston, North worked in a Merchant's office, where he remained until the northern port was closed by British authorities in the fall of 1774.

[4] On May 9, 1776, he was commissioned second lieutenant in Captain John Gill's company of Colonel Thomas Craft's regiment of train artillery.

[5] In 1778 he met Baron Steuben, and the following year was appointed his aide-de-camp, and greatly assisted him introducing his system of discipline in the Continental Army.

As inspector general, Alexander Hamilton, who had worked closely with North during the Revolutionary War, subsequently requested him to serve as his chief of staff.

North began a revision of the army's general regulations in the winter of 1799–1800 before Congress abolished his and other staff appointments as tensions with France diminished in May.

[10] George Washington included North "among the most intelligent and active Officers of the late American Army" in a letter suggesting men for military appointment.

[11] Caesar Russell, an African American Private in the 4th Massachusetts Regiment, served as North's personal servant while aide-de-camp to Baron Steuben.

[12] North and a fellow aide-de-camp, Captain Benjamin Walker, were formally adopted by Steuben and made his heirs.

North was appointed as a Federalist to the United States Senate to fill the vacancy caused by the resignation of John Sloss Hobart and served from May 5, 1798, to August 17, 1798, when James Watson was elected and qualified to succeed.

North was a commissioner and director of the Great Western Turnpike Company which was established by the New York state legislature March 15, 1799.