Maher enlisted on 4 November 1914. He was 5' 5" tall, weighing 136 lbs, with brown eyes and brown hair. He was 22 years and 8 months of age. His occupation was described as "tinsmith", and he is probably the Frederick James Maher, galvaniser, on the electoral roll at 55 Murphy St, Richmond in 1914. His next of kin is given as Margaret Maher, sister, of 24 Ridgeway St, Kensington; in the 1914 electoral rolls she is at that address under the name of Margaret Doris Maher, machinist, and is also registered at 318 Highett St, Richmond.

On Maher's enlistment papers the next of kin is altered to read Lilian Webber of "Tudor", 74 Hotham St, East Melbourne. This address is also mentioned in his file as his address at one point.

Maher embarked from Melbourne on the Runic on 19 February 1915. He suffered an injury on 9 August 1915 at Gallipoli, where he had been since 25 May. His record says that a shell exploded and "blew portion of trench on top of him"; this rendered him "dazed but not unconscious". He was diagnosed with "shell shock" and "sycosis". His symptoms included abdominal pains, headaches, sleeplessness, and it was said that he "gets the jumps". He also had a rash that kept recurring.

He embarked for Australia on the Ascanius, leaving Portland on 17 March 1916, having been found to be unfit for active service. He was judged to be permanently disabled, and the extent of the disability was one quarter of his earning capacity. On 30 April 1916, a medical officer wrote that he was  "improving - will be fit for active service in short period".

At the end of May 1916 and back in Melbourne, Maher was "discharged to the Staff Officer for Invalids", advice of this being sent to his sister, Margaret Doris Dickson (Mrs James Dickson), at 17 Narrak Rd, Balwyn.  Maher was discharged from the AIF on 26 July 1916.

He was awarded a pension of two pounds and six shillings per fortnight on 26 July 1916 (address of his notification was 55 Murphy St, Richmond), reduced to seventeen shillings and threepence from 15 March 1917 (address 162 Murphy St, Richmond); his pension was cancelled from 11 October 1917 (address 74 Hotham St, East Melbourne).

Maher signs for his BWM medal on 23 April 1921, but there is no apparent record of him after that. There is a 9 folio record under his name that is not online (in late 2015); this suggests that he may have tried to re-enlist, without success. He is last mentioned on the electoral rolls (as Frederick James Maher) in 1917 as a galvanizer, living at 55 Murphy St; there is a Frederick James Maher, clerk, at 6 Burnley St, Richmond in 1919, which may or may not be he, but that is the last electoral roll evidence of someone who could be this FJM.