Major General William O'Leary QVRM TD DL VR is retired senior British Army Reserve officer who served as Deputy Commander Field Army.

After serving for seven years as a soldier, O'Leary was commissioned as a reserve officer in the Royal Electrical and Mechanical Engineers ('REME') in 1988.

[2] He went on to be Deputy Brigade Commander of 145 (South) Brigade in 2008, Assistant Commander Theatre Troops in 2011 and Assistant Deputy Military Secretary in 2015.

[5] He was a Colonel Commandant of the Corps of Royal Electrical and Mechanical Engineers until May 2024,[6] and Honorary Colonel of the 103 Battalion REME Army Reserve until June 2024.

[7] After training as an engineering and sales specialist, O'Leary has worked in international business development with MGI Coutier, an automotive systems manufacturer, since the late 1990s.