William Throsby Bridges was born at Greenock, Scotland, on 18 February 1861. As a youth he moved to Canada, where he later entered the Royal Military College but failed to graduate. In 1879 Bridges moved to Australia and joined the civil service, working in Braidwood, Murrurundi, and Narrabri. He returned to military life in 1885, taking a permanent commission in the artillery, and that same year married his wife, Edith. For the next few years he held various positions at the School of Gunnery and attended several gunnery courses in England, passing them with distinction. Bridges served with the British army in South Africa from 1899 until he was evacuated with enteric fever in 1900. In January 1909 he became Australia's first chief of the general staff and the next year was tasked with founding Australia's first military college, the Royal Military College at Duntroon.

By the time the First World War had broken out Bridges had attained the rank of brigadier general and was given the task of raising an Australian contingent for service in Europe. He was promoted to major general in August 1914 and was appointed the commander of the new Australian Imperial Force. Bridges travelled to Egypt with the first contingent in October and started to record his experiences in a diary from early 1915. From this diary we can observe the evolution of planning for the Gallipoli campaign, including his meetings with commanders like Lieutenant General William Birdwood and General Sir Ian Hamilton and with various Australian commanders who would rise to prominence in the years to come.

Bridges' division was the first ashore at ANZAC Cove on 25 April 1915 and very soon after he argued for immediate evacuation, owing to what he saw as a hopeless situation. The force stayed and he began paying routine visits to the firing line, showing disregard for his own safety. On 15 May a sniper's bullet severed his femoral artery and he died three days later on board a hospital ship. He became the only Australian killed in the First World War to have his remains returned to Australia; he was buried at Duntroon.