Lieutenant Colonel John Thomas Eustace (March 9, 1825 – December 25, 1919) was an influential conservative member of the Parliament of the Cape of Good Hope.

Born in 1825 at Grosvenor Place, London, he was the eldest son of Lieutenant General Sir William Cornwallis Eustace, CB KCH and his wife Caroline Margaret, daughter of John King, M.P.

After purchasing a commission in the 60th rifles, he commanded Turkish irregular cavalry in the Crimean War, served in the Middle East, and was appointed Lieutenant Colonel, before emigrating to the Cape Colony.

[1] He served as Vice President of the Chamber of Commerce, married Edith Kate Twentyman in 1860, settled in Wynberg, Cape Town, and had thirteen children.

As such he supported stronger links with the British Empire, a greater roll-out of missionary work in Africa, and a military approach to the Cape Colony's frontier relations.

Though Eustace had the support of many of the conservatives which he led in Parliament, the overwhelming majority in the Cape Colony opposed Wodehouse's move for more direct control and, at the end of the struggle, the Governor returned to London defeated.

[3][4] From 1879, he served as magistrate at Springbokfontein, and a civil commissioner for the Great Namaqualand (modern Namibia), where he informed the Cape Government of the early movements of the future German colonizers.