Garrett was educated at Gormanston College, University College Dublin (UCD) and the Incorporated Law Society of Ireland. His father was T.P. O'Reilly who played on the successful Cavan teams of the 1940s and 1950s and ran his own Solicitor's practice in Ballyconnell before becoming a highly respected Judge.

Garrett followed in his father's footsteps by also representing his County for many years and by becoming a solicitor in 1970.

Garrett has an extensive knowledge of the law providing clients with intelligent and practical advice with the advantage of over 40 years experience as a solicitor.