Joe O'Neill is from Cookstown in Co.Tyrone. He graduated from Queens University Belfast in 1979 after which  he trained as a Chartered Accountant with a leading Belfast based firm of Chartered Accountants. He moved back to Tyrone in 1985, taking up a position as Manager with the firm of Conlon & Co. Upon the merger of Conlon & Co with Coopers & Lybrand in 1988 he was appointed Senior Manager and specialised in Audit of family Companies.

Joe left Pricewaterhouse Coopers (as it then became) in 1992 to co-found McDonald O'Neill & Co.

Joe lectured in Taxation for several years to students studying for the Institute of Accounting Technicians