O'Daire and his fellow Irish volunteers would eventually be placed in the Connolly Column, part of the Lincoln Battalion and the British Battalion at different points, and saw action beginning in 1937. Because of his previous experience in both the Irish war of independence and the civil war, O'Daire was used as an officer. O'Daire served as second-in-command to Peter Daly. O'Daire was wounded early on, getting hit in Lopera near Córdoba in December 1936, but was able to recover reasonably quickly. The Irish would see action in the Battle of Pozoblanco as well as at Guernica before taking part in the Battle of Jarama and then fighting in the Aragon Offensive.