Sully was the son of the portrait painter, Thomas Sully, of Pennsylvania. Alfred Sully graduated from West Point in 1841. During and after the American Civil War, Sully served in the Plains States and was widely regarded as an Indian fighter. Sully, like his father, was a watercolorist and oil painter. Between 1849 to 1853, he became chief quartermaster of the U.S. troops at Monterey, California, after California came under American jurisdiction. Then, Sully created a number of watercolor and some oil paintings reflecting the social life of Monterey during that period.
Sully headed US troops out of Ft. Leavenworth, Kansas, in June 1861 as captain and occupied the city of St Joseph, Missouri, declaring martial law. Violent secessionist uprisings in the city during the early Civil War prompted Sully's occupation.
Also during the Civil War years, the Indian Wars continued in the West. General Sully was sent to command cavalry troops and played an important role in the Indian Wars, becoming known as a successful leader. On September 3, 1863, at Whitestone Hill, Dakota Territory, as reprisal for the Dakota Conflict of 1862, his troops destroyed a village of some 500 tipis that lodged Yankton, Dakota, Hunkpapa and Sihasapa Lakota. Warriors, along with women and children, were killed or captured. The troopers' casualties were small.
Stationed at Fort Randall, South Dakota during the Minnesota Sioux Uprising, aka the Dakota War of 1862, he met a young French-Indian girl of the Yankton Sioux tribe who reminded him of his young Mexican wife whom he had lost to cholera during an epidemic in California. This marriage made him the son-in-law of Saswe, aka François Deloria (Saswe being the Dakota pronunciation of François), a powerful Yankton medicine man and chief of the "Half-Breed band".
Sully's daughter, Mary Sully, was known as "Akicita Win" (Soldier Woman). She became the wife of Rev. Philip Joseph Deloria, an Episcopal priest, aka Tipi Sapa (Black Lodge), a leader of the Yankton/Nakota band of the Sioux Nation. Tipi Sapa is featured as one of the 98 Saints of the Ages at the National Cathedral in Washington, D.C. as the first Dakota Christian minister to his own people. Among their descendants are Vine Deloria, Jr. and Ella Deloria, noted Yankton Sioux scholars and writers.
See also 
- Alfred Sully biography
- Alfred Sully anecdote
- Battle of Whitestone Hill (September 3, 1863), North Dakota State Historic Site
- Rev. Philip Joseph Deloria mentioned in an EpiscopalLife online article
- Litany of Native Saints includes Tipi Sapa's name
- Biography of Ella Deloria, daughter of Tipi Sapa and granddaughter of François des Lauriers (François Deloria, aka Saswe)
- "Alfred Sully". Find a Grave. Retrieved 2009-03-01.
- Pictures of Alfred Sully
- Portrait of Alfred Sully, a Cadet at West Point, 1839, by his father Thomas Sully