Oonagh was admitted as a solicitor in Northern Ireland in 1990 and became a partner in Thompsons in 1999.
Oonagh has developed a specialism in asbestos related disease cases and in 2011 attended before the Finance Committee at Stromont to argue that legislation was necessary and justified to allow people diagnosed with pleural plaques to claim compensation. The damages (Asbestos related conditions) Act (NI) 2011 was subsequently introduced.
Oonagh has represented people with life changing injuries and Thompsons NI is listed as an associated partner with SIA CBIT and Headway.
Oonagh is the representative for Northern Ireland on the EC of the Association of Personal Injury Lawyers and a member of the Pan European Organisation of Personal Injury lawyers, she is also a member of the Belfast solicitors Association.