Educated at South Shields Grammar-Technical School and Exeter College, Oxford, Gary became a history teacher and then was Head of Sixth-Form at Newcastle-under-Lyme School 1983-1987 and Headmaster of Kingswood School, Bath 1987-2008. On his retirement he served as Volunteer Warden at John Wesley's Chapel in Bristol (the New Room) 2009-2019 and was responsible for creating its new Visitor Centre and Museum. He has published five well-received novels and a highly successful children's book, Gospel's Story, but he is best known for his writing and lecturing on early Methodist history. His biography of Charles Wesley in 2008 was reviewed as 'the definitive biography' on Charles. Since then he has published two further equally well-reviewed biographies: John Cennick: The Forgotten Evangelist (2015) and A Tragedy of Errors: the story of Grace Murray (2016), and a number of other highly regarded books, including The Cradle of Methodism (2018), In Their Words (2019), and A School Set Apart (2024). His 'Slavery and Bristol' was reviewed as one of the five best non-fiction books published in 2020. He was a Methodist local preacher for forty years and is currently an Anglican lay reader and he has also written about Christianity, notably Transforming Lives (2008) and A Christian Alphabet' (2021). His latest book, published in October 2025, is Benjamin Ingham: Methodist, Moravian, and Inghamite, the first-ever full-scale biography of this important eighteenth-century evangelist.