Graham Diggins was born in Parramatta, NSW, Australia. He was raised at Merrylands, Dundas, and Ermington, New South Wales. He went to high school at Marsden High, Ermington. He won a Commonwealth Scholarship in 1968 and graduated with a bachelor's degree in Science from Sydney University (1968-70). He was a surface coatings chemist with Sydney firms. He attended Moore College (1975-1977). He received a B.Th (Honours) from the Australian College of Theology in 1978 and a BD (second-class honours) in 1979 from London University. He visited Japan for business in 1987. He received a Diploma in Education from Sydney Teachers College in 1988. He has been a high school science teacher in New South Wales public schools from 1989 to 2018. He enjoys chess, chocolate, apples, liquorice and science fiction.
