It was caused by the death of incumbent MP Robert Fletcher of the Liberal Party and was won by Peter Fraser with a majority of 1,624.

Under the terms of the coalition agreement between Reform and the Liberal's a condition was made not to oppose each other in by-elections for deceased or retiring MP's from their own parties.

Several candidates were approached for the Liberal nomination and eventually William Hildreth, a Wellington City Councillor was selected and endorsed by acting-Prime Minister James Allen.

To many observers, Mack represented "sane Labour" due to his distance from the radical views held by many socialists at the time.

His candidature was put forward by the Protestant Political Association of New Zealand claiming him to be a patriotic individual and not a "Bolshevik" like many of his union colleagues.