[1] The by-election was triggered by the death of Australian Labor Party MP Thomas Thrower, who had died only three months after being re-elected at the 1917 state election.
[3] McGirr was selected overwhelmingly from a broad field that included Iron Trades Federation secretary E. M. Davies, Amalgamated Railway and Tramway Association assistant secretary R. Corish, radical Sydney Wharf Laborers' Union president William McCristal and unsuccessful federal or state election candidates T. Lavelle, I.
[12][13] McGirr won the by-election, finishing 239 votes ahead of McLeod with Foster a distant third, an increase on the Labor majority from the general election.
[14] The pro-Labor National Advocate newspaper in Bathurst described the result as a "magnificent success" that showed that the party was recovering from "the defection of the renegades" in the 1916 party split; they also noted that the result in the usually marginal seat was "the greatest for over nine years" and suggested the margin would have been larger had it not been for Foster's candidacy.
[15] The more conservative Evening News in Sydney downplayed the result, stating "the two parties simply maintained their respective positions: no advantage has been gained by either side", but drew attention to the Nationalist failure to win the seat despite dedicating tremendous resources, stating "the eloquence of nearly every Minister in the New South Wales Government was released upon the electors of Macquarie, but it fell short of success.