Goldsworthy attended Westbourne School, Penarth. After studying ancient and modern history at St John's College, Oxford, he completed a D.Phil in ancient military history from Oxford University in 1994, and then used his dissertation as the foundation of his first book, The Roman Army at War 100 BC - AD 200.

Goldsworthy was a Junior Research Fellow at Cardiff University for two years, and he has taught briefly at King's College London and was an assistant professor on the University of Notre Dame's London programme for six years. His expertise is in Roman history, but he also taught a course on the military history of the Second World War at Notre Dame University. Goldsworthy said that although he enjoyed teaching, he enjoyed writing more and now writes full-time.

Goldsworthy has appeared on History Channel documentaries and the television game show Time Commanders, serving as an expert on battles being fought by the contestants, and he gave a speech about Roman history and politics to the cast of the 2010 Liverpool production of Antony and Cleopatra.

Asked about his philosophy of life, Goldsworthy responded that he was "English, so obviously do not have a philosophy. I am a Christian, though, if you want to know about important beliefs." Goldsworthy lives in South Wales.