He was the eldest of nine children of John Gillies, local lawyer and town clerk, and his wife, Isabella Lillie, daughter of a Glasgow businessman and granddaughter of a Huguenot refugee.

He then went to Manchester, where he worked for Robert Barbour and Sons, with his next brother John taking his place in his father's firm.

John Gillies senior was so committed with various duties that his health suffered and after long discussions, it was agreed to emigrate to Otago, New Zealand.

[6][8] Gillies then represented Mongonui 1870 (elected 30 March 1870; Parliament dissolved 30 December 1870) then Auckland West 1871 to 1875 (resigned); two electorates in the North Island.

When Gillies had visited Wellington, James Hector, manager of the institute, had suggested the appropriateness of establishing branches throughout New Zealand, especially in Auckland.