Cronin a U.S. Marine Corps officer served two tours in Vietnam in Battalion and Force Recon units from 1967-1969, where he was wounded twice. He later returned to the Marines as a commissioned infantry officer for three years.

Following his discharge from the Marines in 1976, Cronin went to Rhodesia and served as an officer on Fire Force with the RLI for about 18 months, participating in counter-insurgency missions. He later transferred to the Selous Scouts, an elite Rhodesian special forces unit, where he served as an operations officer and deployed operational Group second-in-command for a further period.

After leaving Rhodesia in 1980, Cronin pursued higher education, earning a Master’s degree in Middle East Studies in Beirut (where he survived a kidnapping by Hezbollah) and a Ph.D. in Middle East Politics from the University of London. He is the author of the memoir The Bleed: With the Marines in Vietnam and the Rli and Selous Scouts in Rhodesia (2018)