On March 5, 1770 Knox was a witness to the Boston massacre. He was a bookseller in Boston. As Brigadier General Henry Knox took part in the Moland House 
War Council on August 21, 1777. He was in charge of the artillery. In the months before Knox was almost displaced of his position in charge of artillery by a Frenchman named Ducondray. Washington wrote Congress on behalf of Knox on May 31, 1777: “General Knox, who has deservedly acquired the character of one of the most valuable officers in the service, and who combating almost innumerable difficulties in the depar
tment he fills has placed the artillery upon a footing that does him the greatest honor; he, I am persuaded, would consider himself injured by an appointment superseding his command, and would not think himself at liberty to continue in the service. Should such an event take place in the present state of things, there would be too much reason to apprehend a train of ills, such as might confuse and unhinge this important department.”
Knox was elected Secretary of War by Congress in 1785, and in 1789 he was appointed Secretary of War in President Washington’s new cabinet.