Coffin, Charles. The Life and Services of Major General John Thomas. First. New York: Egbert, Hovey & King, 1844.
The Coffin biography is the best available and can be found on-line.
Broadwater, Robert P. American Generals of the Revolutionary War: A Biographical Dictionary. Jefferson: McFarland, 2012.
Headley, J.T. Washington and His Generals. Home Library. New York: A. L. Burt Company, n.d.
Memoirs and Papers
John Thomas papers, Massachusetts Historical Society.