Peter was a son of George and Annie Slavin of West Wallsend NSW. He became a teacher, receiving his first appointment in 1912. Three years later he was appointed to Bonshaw Public School, north of Inverell. At the foundation meeting of the Bonshaw Rifle Club in July 1915 he was elected Secretary. After just a few months at Bonshaw, Peter enlisted at Newcastle NSW. He was twenty two and a single man. Perhaps he was influenced by the huge recruiting campaign underway at the time.

Peter joined the 34th Battalion, B Company and sailed from Australia for England on HMAT A30 Hororata in May 1916. Five months later he was promoted to Lance Corporal and sent to France where he served with the 3rd Division Signals Company. He returned home on the transport ship Borda and was discharged in June 1919. His brother George also served during the War.

Peter returned to teaching and lived in Sydney where he died in 1980. His name is inscribed on the West Wallsend Soldiers Memorial and the Bonshaw Honor Roll.