During the Civil War, he was briefly lieutenant colonel of the 7th Infantry Regiment (United States).

[4][7] He was appointed as a cadet at the United States Military Academy at West Point, New York, on July 1, 1825.

[1] Cady was promoted to first lieutenant, 6th United States Infantry Regiment, on December 31, 1836.

[1][4] Captain Cady commanded one of the five parties of one hundred U.S. soldiers each who stormed the flour mill at the Battle of Molino del Rey but who were repulsed with numerous casualties.

[10] Cady was appointed brevet major, September 8, 1847, for gallant and meritorious conduct in the Battle of Molino del Rey.

[4][9][11] Cady was a member of the Aztec Club of 1847, which was founded as a military society of officers who served with the United States Army in the Mexican–American War.

[12] After the Mexican–American War, Cady was assigned to garrison duty at Jefferson Barracks Military Post, Missouri, in 1848 and Fort Scott, Kansas, also in 1848.

[14][15][16][17] Cady was promoted to lieutenant colonel, 7th Infantry Regiment (United States), June 6, 1861.

[4][9][11] During the Civil War, Cady served in command of the District of Oregon from October 23, 1861, to April 7, 1862.

[4][7][9][11] Nonetheless, Cady commanded the Draft Rendezvous at New Haven, Connecticut, from March 4, 1864, to October 25, 1865.