John was the youngest of three sons born to John Jacob Astor V, 1st Baron Astor of Hever (1886–1971) and Lady Violet Mary Elliot-Murray-Kynynmound (1889–1965). He had two elder brothers, Gavin Astor, who inherited his father's barony, and Hugh Astor. His mother had two children, Mary Petty-Fitzmaurice, and George Petty-Fitzmaurice, from her first marriage to Lord Charles Petty-Fitzmaurice who was killed in action at Ypres. His elder half-brother George later became the 8th Marquess of Lansdowne