Gillies was educated at local schools and in 1882 went with his parents to the Village of Tintenbar in the Richmond River country.

[2] Gillies was assistant-minister for justice in the Thomas J. Ryan ministry from 25 April 1918 to September 1919[1] and for a few weeks until 22 October, was secretary for agriculture and stock.

He held the last position in the Ted Theodore ministry from October 1919 till February 1925,[2] and his practical experience as a farmer was found to be of great use.

On the resignation of Theodore, Gillies became premier on 26 February 1925, taking the positions of chief secretary and treasurer,[2] and vice-president of the executive council.

Gillies was a man of moderate views and he found the more extreme section of the party very active, and he was beset with anxieties.