Maguire was born in North Adelaide, the eldest son of John McGuire and his wife Mary, née Grant (c. 1831 – 16 April 1910),[2] who both emigrated aboard Grand Trianon in 1855, but married in Clare, South Australia on 27 November 1855.
In 1888 he was appointed Traffic Superintendent of the South-Eastern Division, the move to Kingston SE coinciding with the birth of their third son, Grant Augustine.
[6][7] The following year he was in the North again, as Superintendent of the Western Division in Petersburg, in charge of the northern system, which mostly consisted of the Broken Hill–Port Pirie line, arguably the most difficult section of railway in Australia to organise; keeping water supplies available to the steam locomotives in that dry and barren country being a constant challenge.
[5] In 1910, in the shakeup following McArthur's retirement, McGuire was promoted to Superintendent of Station Services in Adelaide, in charge of all broad gauge lines[8] a position he held until 1915, when he succeeded J.
He was appointed colonel in the Australian Staff Corps in 1917, a rank he held until his death, being largely responsible for developing national military transportation.
[5] McGuire was a devoted Roman Catholic, which fact was occasionally used against him, but there was no denying his loyalty to the State and the British Empire, as witness his personal losses in the Great War.