Born in Sydney on 10 December 1916, Waddy was the son of first-class cricketer Edgar Lloyd Waddy and his wife Lottchen, and great-grandson of General Sir Richard Waddy, KCB.[2][3] His four siblings included a sister and three brothers.[1] Edgar Waddy established the real estate firm of E.L. Waddy & Son in Rose Bay, which John joined as a clerk after completing his education at the King's School, Parramatta.[3][4] He married Vera Nellie May (Ve) Dengate on 21 July 1938.