Dr O’Donnell qualified at the National University of Ireland, Galway, in June 1978 and completed his General Practice training in Portsmouth in 1982.
He worked in tertiary referral medicine in Baghdad, Iraq from 1984 to 1988 followed by a cardiology research post at Wexham Park Hospital (UK) involving the first use of thrombolysis in acute myocardial infarction.
This led to a career in the pharmaceutical industry involving novel treatments for ischaemic heart disease. He continued as a GP and was involved in the development of new medicines up to 1998 at which time he returned to full-time general practice in Slough and had a key interest in clinical governance and education in primary care. In 2007 he became the Slough Locality Lead and shortly after in 2008 he became Chairman of the Clinical Executive Committee at Berkshire East PCT.
He is also a member of the NHS Commissioning Board “Sounding Board” and has been involved in drawing up plans for the Commissioning Assembly.