Having served in New York's militia before the Civil War, he was commissioned as a second lieutenant in the Union Army's 1st Artillery Regiment once hostilities commenced.

After leaving the Army in 1871, Crosby worked as an engineer, designing and supervising the construction of lighthouses, breakwaters, and other marine projects.

He served as U.S. Consul in Florence, Italy from 1876 to 1881, Governor of the Montana Territory from 1883 to 1884, U.S. First Assistant Postmaster General from 1886 to 1889, and as New York City school commissioner from 1889 to 1891.

[6] At the beginning to the American Civil War he joined the Union Army and, having previous experience with the New York State Militia, was commissioned a second lieutenant in the First Artillery.

[5] In 1862, Crosby was transferred to the Department of the Gulf and following the battles of Fort Bisland, Irish Bend and Vermilion Bayou was brevetted a captain for gallantry.

During the Red River Campaign, Crosby earned a letter of thanks from President Abraham Lincoln for carrying dispatches through enemy territory to Admiral Farragut.

Despite this level of dedication, the Republican governor still managed to antagonize the territory's Democratic majority through liberal use of his veto power.

Other activities pursued by the governor were a strong anti-crime policy, opposition to polygamy, and an effort to reduce lands held by Native Americans.

He was also active in the Grand Army of the Republic, Loyal Legion, Sons of the Revolution, and a variety of Washington, D.C., and New York City social clubs.

On January 20, 1913, while he was in his sick bed, one of his servants suddenly became crazed and he was forced to fight off and subdue the knife wielding valet.

[17] His grandson was Henry Sturgis Crosby (1898–1929),[18] a bon vivant, poet, and publisher who for some epitomized the Lost Generation in American literature,[19] who was married to Mary Phelps Jacob (1891–1970).