He did not seek re-election for the assembly in 1860 but in 1861 became a member of the South Australian Legislative Council. In 1870 he was one of the South Australian delegates to the intercolonial conference held at Melbourne. In 1871 he resigned from the council, and the following year was returned to the South Australian House of Assembly for Sturt. He joined the seventh Henry Ayers ministry as Treasurer of South Australia in March 1872, holding the position until Ayers resigned in July 1873. John Barrow was also the first Mayor of the newly created municipality of the Town of Unley, and was an active member of the South Australian Free Rifle Corps. In mid-1873, Barrow's health declined, and though he went to the intercolonial conference at Sydney as one of the South Australian delegates in the hope that change of scene might lead to its improvement, it continued to deteriorate; he died in Adelaide on 22 August 1874 of an effusion on the brain. He was married twice and left a widow, three sons and three daughters. Barrow left behind him a reputation in his own time as a speaker and journalist. Barrow was married to Sarah Barrow née Liversedge (c. 1814 – 4 October 1856). Their children included: On 15 August 1865 Barrow married again, to Mary Burden (died 10 May 1907), the widow of Philip H. Burden (c. 1823 – 3 March 1864), and adopted her children, who included   Mary married again, to Benjamin Cowderoy on 25 November 1878.