[1] He came to New Zealand as a young boy on the Prince of Wales, arriving on 3 January 1843 in Wellington with his parents John and Henrietta, his younger brother Sydney and a sister who was born during the journey.
Pharazyn left after two years but Johnston stayed with Willie Levin until 1878 when following his own father's retirement he moved back to his brother Charles in Johnston & Co, the firm their father had started, the pair making it a major importing and exporting business with branches throughout central New Zealand.
[2] He acquired Castlepoint station[3] in the Wairarapa in 1876 while with W H Levin & Co and inherited further property in southern Hawkes Bay from his father.
He bought a 1200-acre estate near Awahuri in the Manawatū District in 1888 and built a large house, Highden, there before the turn of the century.
[2] Johnston was a cabinet minister in 1881–84 in the Hall, Whitaker and Atkinson Ministries; Postmaster-General, Telegraphs and Public Works.