Captain John Byron (1755-91), born at Plymouth, was the eldest son of Admiral the Hon. John Byron (1723-86) — known in the Royal Navy as "Hardy Byron" or "Foul-weather Jack" — by his marriage (1748) with Sophia Trevanion of Carhais, in Cornwall. The admiral, next brother to William, fifth Lord Byron, was a distinguished naval officer, whose
Narrative
of his shipwreck in the
Wager
was published in 1768, and whose
Voyage round the World
in the
Dolphin
was described by "an officer in the said ship" in 1767. His eldest son, John Byron, educated at Westminster and a French Military Academy, entered the Guards and served in America. A gambler, a spendthrift, a profligate scamp, disowned by his father, he in 1778 ran away with, and in 1779 married, Lady Carmarthen, wife of Francis, afterwards fifth Duke of Leeds, née Lady Amelia d'Arcy, only child and heiress of the last Earl of Holderness, and Baroness Conyers in her own right.
Captain Byron and his wife lived in Paris, where were born to them a son and a daughter, both of whom died in infancy, and Augusta, born 1783, the poet's half-sister, who subsequently married her first cousin, Colonel George Leigh. In 1784 Lady Conyers died, and Captain Byron returned to England, a widower, over head and ears in debt, and in search of an heiress.