O'Leary achieved his award for single-handedly charging and destroying two Imperial German Army barricades defended by machine gun positions near the French village of Cuinchy, in a localised operation on the Western Front during World War I.

Aged 16 and unwilling to continue to work on his parents' land, Michael O'Leary joined the Royal Navy, serving at the shore establishment HMS Vivid at Devonport for several years until rheumatism in his knees forced his departure from the service.

[1] O'Leary served three years with the Irish Guards, leaving in August 1913 to join the Royal North-West Mounted Police (RNWMP) in Saskatchewan, Canada.

[1] At the outbreak of the First World War in Europe during August 1914, O'Leary was given permission to leave the RNWMP and return to Britain in order to rejoin the army as an active reservist.

Innes regrouped the survivors and, following a heavy bombardment from supporting artillery and with his own company providing covering fire, assisted the Coldstream Guards in a second attack at 10:15.

Charging past the rest of the assault party, O'Leary closed with the first German barricade at the top of the railway embankment and fired five shots, killing the gun's crew.

Continuing forward, O'Leary confronted a second barricade, also armed with a machine gun 60 yards (55 m) further on and again mounted the railway embankment, to avoid the marshy ground on either side.

[1] Tributes came from numerous prominent figures of the day, including Sir Arthur Conan Doyle who said that "No writer in fiction would dare to fasten such an achievement on any of his characters, but the Irish have always had a reputation of being wonderful fighters, and Lance-Corporal Michael O’Leary is clearly one of them."

[8] O'Leary was further rewarded for his service, being advanced to a commissioned rank as a second lieutenant with the Connaught Rangers,[9] and he was also presented with a Russian decoration, the Cross of St. George (third class).

[12] Leaving his wife Greta and their two children in Britain, O'Leary returned to Canada in March 1921 with the purported intention of rejoining the RNWMP, newly renamed the Royal Canadian Mounted Police.

For unknown reasons, this plan came to nothing and after some months giving lectures on his war service and working in a publishing house, O'Leary joined the Ontario Provincial Police, charged with enforcing the prohibition laws.

By 1932, O'Leary was living in Southborne Avenue in Colindale, had regained his health and found employment as a commissionaire at The May Fair Hotel in London, at which he was involved in charitable events for wounded servicemen.

In 1945, he was discharged from the military as unfit for duty on medical grounds at the rank of major and found work as a building contractor in London, in which career he remained until his retirement in 1954.

As a Victoria Cross recipient, O'Leary joined the VE day parade in 1946, but at the 1956 Centenary VC review his place was taken by an imposter travelling in a bath chair.