Dr McKenna trained at QUB, qualifying in 1992. He then completed his postgraduate training in Belfast City Hospital, Mater and Craigavon before completing his GP trainee year in Glasgow.
On returning to Belfast he undertook GP non principal roles and was Chair of the Northern Ireland Sessional Doctors Association from 1999 until 2002. He then took on a single handed practice on the Falls Road in Belfast where he continues to practice.
Dr McKenna has an interest in diabetes care and prescribing and was Chair of the North & West Belfast primary care prescribing committee which subsequently evolved into the Belfast group which he chaired from 2009 until Jan 2017.