On 3 August 1905, Hackett married the 18-year-old [[Deborah Vernon Hackett|Deborah Vernon Brockman]] (1887–1965). TheyHe confided in his political ally Walter James, "This is in the strictest sense a 'marriage de convenance'".<ref>William Coleman,''Their Fiery Cross of Union. A Retelling of the Creation of the Australian Federation, 1889-1914'', Connor Court, Queensland, 2021, p. 64.</ref> The couple had four daughters, and a son also called John. John (1910–1997) also became [[John Hackett (British Army officer)|Sir John Hackett]], a popular and distinguished [[General (United Kingdom)|General]] in the [[British Army]]. After she was widowed, Lady Hackett remarried to become Lady Moulden, and finally – after an honorary doctorate and a further widowhood – married Basil Buller Murphy to become Dr. Deborah Buller Murphy.
A daughter [[Patricia Hackett]] (1908–1963) followed her father into the legal profession, and is today remembered for the Patricia Hackett Prize awarded by the [[University of Western Australia]] and endowed in her memory in 1965.<ref>William Wilde ''et al'', ''The Oxford Companion to Australian Literature'' Oxford University Press, Melbourne 2nd edition 1994 {{ISBN|0 19 553381 X}}</ref>
