William John Fergusson was a solicitor and politician from New South Wales, Australia.

He was a practicing solicitor in Sydney before entering politics,^[1] having been admitted in March 1876.^[2] He was elected to the New South Wales Legislative Assembly for Glen Innes, at the 1880 election, serving until 1887.^[3] Fergusson supported William Clarke's attempts to form a third party, however these failed with no other parliamentarian joining them,^[4] and Fergusson sat with the opposition to the ministry of Patrick Jennings.^[5] Political parties emerged in New South Wales in 1887, divided on fiscal lines, and despite his previous opposition to Jennings, Fergusson stood as a Protectionist candidate at the 1887 election for Wentworth, finishing a distant fourth.^[6]

Very little is known of his biography, with his parliamentary biography bereft of the usual details.^[1] On 14 May 1881 he married Emily Maud Mary née York.^[7] He was a partner in the legal firm Fergusson and Broad and by 1893 the partnership was in difficulty, having received £1,000 from a client and £500 went missing. The explanation offered by his partner was that Fergusson, who was in England, had sent a draft and the money lodged in the bank had been used to pay that draft.^[8] He was a trustee of the will of James York, and in 1893 the beneficiaries, including his wife sought to have him removed as a trustee and to account for the money received by him.^[9]

It appears that he never returned to Australia,^[10] and his wife obtained a divorce in 1912 on the grounds of desertion.^[11]

Fergusson is believed to have died in New Zealand.^[1]