In 1832 Hart was in command of the schooner Elizabeth, a sealer operating from Tasmania and visiting Kangaroo Island and Gulf St Vincent.

Early January 1838 he was "on the River Murray near Mount Hope" (perhaps the Lachlan near Hillston) and foresaw the great thoroughfare it would become in the second half of that century.

In January 1843 Hart sailed to England in command of the South Australian Company's ageing barque Sarah and Elizabeth, delivering it to London for sale.

Aboard as a passenger was the explorer John Hill, from whom Hart had just purchased Section 2112 at Port Adelaide, in partnership with Jacob Hagen.

He was Treasurer of South Australia in the Baker ministry which lasted only a few days in August 1857, and held the same position in the Hanson cabinet from 30 September 1857 to 12 June 1858 when he resigned.

One newspaper obituary gave the opinion that Hart had been unfairly criticised in several of his decisions (and had been subsequently vindicated) and should have been given credit for the Overland Telegraph Line rather than Sir Henry Ayers.

[8] John Hart died suddenly on 28 January 1873, while chairing the third annual general meeting of the Mercantile Marine Insurance Company at the Adelaide Town Hall, leaving a widow and a large family.