Stephen Dandridge Kennedy was born May 25, 1834, in Berkeley County, Virginia (present-day West Virginia) to Anthony and Sarah Dandridge Kennedy. He came from an illustrious political family that traced its roots to 17th-century Tidewater Virginia. His father served in the Virginia House of Delegates from 1839 to 1843 and represented Maryland in the United States Senate from 1857 to 1863, while his uncle John Pendleton Kennedy was Secretary of the Navy under President Millard Fillmore. 

Kennedy received his early education in Martinsburg, Virginia, before entering the Virginia Military Institute in July 1850. He proved deficient in mathematics and left the school after only a year, enrolling at the University of Virginia in 1851. He was an indifferent student, and the faculty minutes frequently list him as absent, delinquent, “making no progress,” and “doing nothing” in class. The Chairman admonished him in February 1852, but to no avail. That June, the faculty agreed it would be “inexpedient” for Kennedy to return to UVA. Instead, he re-entered VMI, graduating in 1853.

He earned a medical degree from the University of Maryland in 1855 and began practicing medicine in Baltimore. He was a visiting physician at the Baltimore City and County Almshouse and served as a delegate to the 1857 National Convention of Physicians. On May 9, 1861, four weeks after the Confederate attack on Fort Sumter, Kennedy enlisted as an assistant surgeon in the United States Navy. He spent the next two years in the West Gulf Blockading Squadron, assigned to Admiral David Farragut’s flagship, the USS Hartford. He was present at the battles of Port Hudson, Grand Gulf, and Warrenton in the spring of 1863. In August 1863, he was assigned to the Naval Hospital in Washington, where he remained for more than a year.

On November 24, 1863, Kennedy married 22-year-old Frances Howell, the granddaughter of War of 1812 hero George Armistead. She died in October 1864, shortly after the birth of their daughter Frances. Kennedy resigned from the navy that month “on account of domestic affairs of a private nature.” He was reappointed in January 1866, receiving a commission as a surgeon. From 1867 to 1868, he served aboard the USS Lackawanna in the North Pacific Squadron, and in August 1867 his captain William Reynolds took formal possession of the Midway Islands for the United States. The following year, he witnessed the eruption of Kilauea, which triggered the largest recorded earthquake in Hawaiian history.

Kennedy returned to America in 1869, and on June 22 he married his cousin Mary Selden. They had four children: Anthony (1873), Mary (1875), Margaret (1877), and Agnes (1881). From 1871 until 1878, he moved between the Pacific and Atlantic fleets, serving aboard the Ossipee, the Powhatan, the Monongahela, and the Lackawanna. In January 1879, however, he was court martialed and discharged for being drunk on duty. Two years later, he was readmitted to the navy, and on October 15, 1881, he received a promotion to medical inspector.

In October 1883, he faced a second court martial for drunkenness and absence without leave. His commander, Kennedy pleaded for leniency, observing that he had been at sea for almost eight months and suffered rheumatism, debility, and recurrent malaria. He had begun using alcohol to manage his illness and exhaustion, claiming he was “compelled to resort to stimulating medicine for support.” For years, he explained, he had “made an increasing and, up to the time charged, a successful fight against intemperance.” He asked the court to help him “fight against this sin, and give me one more chance to assert my manhood and honor.” Unmoved, they found him guilty of all charges and dismissed him from the navy.

Kennedy joined his family in Annapolis and resumed his private medical practice. Around 1897, he moved to Warrenton, Virginia, where he died of senility and chronic diarrhea on September 3, 1914.