Samuel McDowell was born in the Province of Pennsylvania on October 29, 1735. He was the son of Captain John McDowell and grandson of Ephraim McDowell, a Scots-Irish patriot in the English Revolution of 1688. Captain McDowell relocated his family to Virginia in 1737. Samuel McDowell was well-educated in his youth, at one time studying under Archibald Alexander. In 1743, his father died and he inherited the entire estate, according to the tradition of primogeniture, but chose to divide the estate with his brother and sister.