On 15 August 1914, MacLaurin joined the Australian Imperial Force as a full colonel and given command of the 1st Infantry Brigade.

By this time a crisis was developing and Major General William Bridges was ordering units to fill gaps almost as soon as they arrived ashore.

During the afternoon of 27 April 1915, when a Turkish counterattack threatened, Major Irvine collected 200 stray men in Monash Valley and was about to send them forward when the news arrived that the need for them had passed.

Unaware of Irvine's fate, MacLaurin was in the act of warning soldiers to keep under cover when he too was shot dead, from the same point, possibly by the same Turkish sniper.

His eldest brother – listed as his next of kin and one of the executors of his will – was Dr. Charles MacLaurin (1872–1925), a lecturer in medicine at the University of Sydney and the author of Postmortem and other books.