In 1865 he bought a house in Octavia Street, St Kilda, and on 22 August 1871 he married his cousin, Mary Richmond, at the Wesley Church on Lonsdale Street. King never fully recovered from the privations suffered while on the expedition, and in 1869 his health began to deteriorate. During November and December 1871 he was so ill he was cared for at his sister's house in Drummond Street, Carlton. He returned home to St Kilda and died prematurely of pulmonary tuberculosis on 15 January 1872 aged 33. His pall-bearers were Ferdinand von Mueller, Dr David Wilkie and Inspector James M Gilmour. He is buried in the Melbourne General Cemetery.