John Kavanagh Leacy was born on 22 May 1912 to George Hugh and Mary Leacy (nee Cavanagh) near Rockhampton, Queensland, the tenth of fourteen children. Mary Leacy died in 1918, and George Hugh committed suicide in 1922, when John was ten years old. The four youngest Leacy children became wards of the state after their father’s death. John Kavanagh lived with the McCauley farming family and the Diamantina Receiving Depot and Infants' Home.

After turning 18, Leacy worked as a stockman and a labourer, eventually making his way to Sydney. During this period, he worked for an immigrant couple near Buaraba, where he picked up some German language skills. He enlisted in the Second Australian Imperial Force on 7 November 1939, joining the 2/1st Battalion, 16th Brigade, 6th Division. After training at Ingleburn Camp, Leacy and the 2/1st embarked for overseas service in early 1940.

Leacy served with the 2/1st during its campaigns in North Africa against Bardia and Tobruk in early 1941. The unit was then redeployed to Greece, where he saw combat against Germany before the Australian forces were withdrawn to Crete. Leacy and the 2/1st fought in defence of Rethymno airport, but were overwhelmed by German paratroopers and reinforcements. The battalion surrendered and Private Leacy became a prisoner of war, although he was initially reported as missing-in-action.

Leacy was sent, along with other captured men from Crete, to Stalag XIII-C near Hammelburg, Bavaria. John Leacy was assigned Gefangenennummer (prisoner number) 10233. Due to his fluency in German and his experience as a stockman, Leacy was selected to work at an Arbeitskommando, a sub-camp under the prisoner-of-war camps wherein enlisted POWs worked on farms and in non-military industries. He worked in the camp at Waltershausen until mid-1944.

In August 1944, Leacy was court-martialled by the German military authorities. The official charges were of continuously disobeying orders, ‘causing damage to the Reich and endangering its safety’. He , along with four other men, were accused of leaving their work camps and having sexual relationships with German women in the town. Three of the women were married to German soldiers.

Leacy was sentenced to three years hard labour, serving his sentence in solitary confinement. On 6 April 1945, Stalag XIII-C was liberated by the US 14th Armored Division. Leacy returned to the village of Waltershausen with companions from the camp for several weeks before travelling to England. During the stay at Waltershausen, he visited the nearby Buchenwald concentration camp and acquired reports of the locals’ visit to the camp in English and German.

After the peace in Europe, Leacy met his wife, Betty Winifred Martin, while recovering in England. They were married within two weeks. He then returned to Australia; during the return journey, the war in the Pacific ended. He was discharged after the disbanding of the 2/1st, on 11 December 1945.

After settling in Sydney with his new wife, Leacy worked as a labourer before becoming a special constable and then a police officer. He died on 17 August 1991 at the age of 79. He was survived by his wife, Betty Winifred, their three children, and three grandchildren.