During the Spanish Civil War, he met and married Salaria Kea, an African-American nurse, who was also volunteering her services.

[1][2] His father fought as part of the Royal Irish Regiment of the British Army during World War I. O'Reilly describes his childhood as one of poverty and boredom in rural Ireland.

Soon, O'Reilly saw a newspaper advertisement requesting volunteers to go and fight on behalf of the government/republicans in the now-begun Spanish Civil War.

[1] In a 1975 interview, O'Reilly described that a French volunteer officer named LaSalle was executed for treason after the battle by the republican leadership.

[3] On 11 January 1937 O'Reilly's company was redeployed to Madrid to take part in the Second Battle of the Corunna Road, which involved thousands of troops from both the republican and nationalist sides.

However, many Irish volunteers had split off from this unit to form their own; the Connolly Column which attached itself to the American Lincoln Battalion.

Survivors of earlier engagements were kept in reserve and thus O'Reilly was assigned Quartermaster of the British cookhouse, a role that quickly left him disillusioned with his choice.

[1] As the Battle of Jarama commenced in February 1937, O'Reilly offered to work as an ambulance guard at Morata de Jalón close to the battlefront.

It was during this time, while working in and around American No.1 Base Hospital at Villa Paz, that O'Reilly encountered the new head nurse Salaria Kea who had just arrived from New York City.

[1] O'Reilly and Kea continued to serve the Republican forces in the Civil war, providing medical services.

[1] Within weeks of the relocation, Kea alongside many other medical staff were sent back to the United States as they suffered from Post-traumatic stress disorder.

[1] During this period O'Reilly sent a letter home to his father, explained he felt he could not return to Ireland with his new wife without them facing discrimination.

[3][4] The unit received training at Camp Swift in Texas before being shipped to North Africa in November 1943, and from there to Frome in Somerset, England, where they were kept in waiting for D-Day.

[1] The Second war powers act of 1942 made it much easier for non-citizens who served in the American military to obtain citizenship after their service had ended.

[1][4] Additionally, O'Reilly and Kea were occasionally harassed by the FBI because of their involvement in the Spanish Civil War, fearing that they were communists.

[1] Mindful of reactions to their interracial marriage, O'Reilly and Kea lived in a Jewish neighbourhood until the mid-1950s, before moving to Grace Avenue in the Bronx.

While they enjoyed the comfort of Kea's family, they also experienced harassment from the Ku Klux Klan on Sunday after they attended Catholic Mass together.