[2] He and the American economist James Edward Le Rossignol of the University of Denver published State socialism in New Zealand in 1910.

A reviewer called the book "an illuminating study of the remarkable series of instructive experiments in socialistic legislation, for which New Zealand has become conspicuous, together with that Australian Commonwealth, which is its nearest neighbour.

[2][6][7] Downie Stewart stood in the 1935 general election as an Independent United-Reform Coalition candidate, losing to Labour's Dr Gervan McMillan.

In July 1934, he became the first chairman of the newly formed New Zealand Institute of International Affairs, the local branch of Chatham House.

[8] He ceded that position to Bill Barnard, the speaker of the House, the NZIIA merged with the local branch of the Institute of Pacific Relations in late 1939.