Around 1862, his father requested he change his first name to Llewellyn for family reasons after joining the army.

[1][2][3] Haskell was receiving his education in Heidelberg, Germany when he decided to return in 1861, and enlisted in the 14th New York Volunteer Infantry Regiment as a private.

Haskell was the only member of General Prince's staff to escape with his life; he was hospitalized for four months after the battle.

[4][5][10] On June 4, 1868, he married Emmeline "Emma" A. Gilmore (1849–1925) at Llewellyn Park, in an open air ceremony.

[11] The couple had two sons:[12] He died in San Rafael, California, on November 26, 1929, and his remains were cremated.