Jackson was born in Lurgan, County Armagh, Northern Ireland, the son of a Church of Ireland rector (latterly appointed Archdeacon of Elphin & Ardagh), and educated at Ballinamallard Primary School and Portora Royal School, Enniskillen. He achieved the Louis Claude Purser Entrance Scholarship to Trinity College, Dublin. As only a Junior Freshman, he was elected as a Scholar of the College, the greatest undergraduate achievement in 1979 in classics. As a Senior Freshman was awarded the Bishop Berkeley Gold Medal for Greek. As a Sophister, he achieved a First in the Moderatorship Part I along with a Mullins Classical Exhibition, before finally taking a first class Moderatorship II in Classics and a Gold Medal, and graduating with a B.A. in 1979. He incepted to M.A. in 1982.