He served in the cavalry during the American Revolution, seeing combat in the Battle of Bunker Hill and in the engagement at Elk River, he received seven sabre cuts on the head, and was left on the field as dead.

Kirby practiced law in Litchfield, Connecticut and, in 1787, Yale gave him an honorary Master of Arts degree.

President Thomas Jefferson appointed Kirby Supervisor of Internal Revenue for Connecticut, a position he held until September 1802.

He went directly to his new post, Fort Stoddert, on the Alabama River north of Spanish-held Mobile, near the present Mount Vernon.

He lived only a few months, dying of fever after being appointed by President Jefferson as the new Judge of the Superior Court of the Territory of Orleans.