William John Foster

William John Foster (13 January 1831 – 16 August 1909) was a politician and Supreme Court judge in colonial New South Wales, Attorney General from 1877 to 1878.

Foster was born in Rathescar, County Louth, Ireland, the son of Rev. William Henry Foster of Loughgilly, County Armagh, and his wife Catherine, Hamilton.

Foster arrived in Sydney in August 1854, and for the first three years of his residence in New South Wales devoted himself to agricultural pursuits. He then studied law, and was called to the colonial bar in 1858, when he entered on the practice of his profession. Foster was made Queen's Counsel in 1886, and in the following January he again took office as Attorney-General under Sir Henry Parkes, but resigned in May 1887, on the ground that his prior claim to the vacant Puisne Judgship had been slighted. The following February he accepted appointment as a judge of the Supreme Court. Foster married in 1854 Matilda Sophia, daughter of John Williams, of Landigige, Pembrokeshire. He on several occasions refused appointment as a judge of the District Court, and declined nomination to be the Speakers of the Assembly in 1887.

Foster died in Valley Heights, New South Wales on .