He commanded Brigade 1, Division 3 of the Cavalry Corps (Union Army) from June 28, 1863 to July 3, 1863, when he was mortally wounded and died at the Battle of Gettysburg.

He was nominated by President Abraham Lincoln for appointment to the grade of brigadier general on June 29, 1863 but was not confirmed by the United States Senate before his death at Gettysburg.

[1] John Farnsworth was a Union Army colonel who also commanded cavalry brigades (September 1862 to February 1862) and was nominated for appointed to the grade of brigadier general (November 1862).

[1] A member of the Chi Psi Fraternity, Farnsworth was expelled from the University of Michigan following a drinking party in which a classmate died after being thrown from a window.

On June 29, 1863, just two days before the battle, President Lincoln nominated Farnsworth to the grade brigadier general of volunteers but the appointment was never confirmed by the United States Senate.