Tallmadge ranked as Major in the 2nd Continental Light Dragoons and was commissioned on June 20, 1776.
He was given the position of Director of Military Intelligence by General George Washington. Tallmadge helped to assemble a network of spies known as the “Culper Spy Ring”
Tallmadge spent the winter of 1777 and into January 1778 with George Washington at Valley Forge. General Washington was so impressed with Tallmadge, that he assigned Tallmadge the task of spymaster during this time. The Culper Spy Ring was established in 1778 during the British occupation of New York City. The spy ring operated mostly in New York City, Long Island and Connecticut, beginning in late October 1778. The Culper Spy Ring used a numerical substitution code that was Tallmadge developed. The spy ring kept Washington informed on the movements of the British troops. The Culper Ring was further involved in revealing the betrayal of one of Americas most famous traitors, Benedict Arnold.
Tallmadge directly participated in the battles of Trenton, Battle of Fort St. George, Battle of Monmouth, Battle of Stony Point, and the Siege of Yorktown in defense of our new nation.
Tallmadge later serve at Washington’s headquarters from March 1781 until the Continental Army was disbanded in November 1783. He was ultimately promoted to the rank of Lieutenant Colonel on September 30, 1783
Benjamin Tallmadge served as postmaster of Litchfield, Connecticut from 1792 until he was elected to Congress in 1801 and served in that role until 1817. He was the first President of the Phoenix Branch Bank and also the first Treasurer of the Society of the Cincinnati in Connecticut. He later served as President of the Connecticut Society. Tallmadge engaged as an importer of mercantile pursuits until his death on March 7, 1835.