Dr Mainie works as a Consultant Gastroenterologist in the Ulster Independent Clinic. He also works as a Consultant Gastroenterologist in the Belfast Trust. Dr Mainie qualified from Queens University Belfast in 1995. He trained in both Gastroenterology and General Medicine. Dr Mainie completed an advanced therapeutic endoscopy and oesophageal motility fellowship in Medical University South Carolina, Charleston, SC, USA 2003 -2006. He also completed his MD in Reflux disease and Impedance-pH testing in Medical University South Carolina.

Dr Mainie provides a tertiary referral service for upper GI patients including complex reflux patients, early oesophageal and stomach cancers, oesophageal motility disorders, endoscopic Ultrasound for cancer staging and therapeutic interventional endoscopy. He provides a regional service for endotherapy (including endomucosal resection and radiofrequency ablation) for Barrett's oesophagus.

Dr Mainie recently represented N Ireland as a regional expert as part of an international group for quality endotherapy for Barrett's oesophagus. He also does General Gastroenterology including the treatment of inflammatory bowel disease and irritable bowel syndrome. Dr Mainie does over 1200 upper and lower endoscopies a year.

He is very active in both national and international research and regularly reviews for international journals. He was the principal Investigator on the SPIT study, BOSS study, HALO registry, DELTA project in the use of cytosponge for Gastroesophageal reflux disease disease and Barrett's oesophagus and also the Hemopspray registry. Recently completed research in the International HALT study for upper GI bleeding. Principal Investigator for Eosinophilic Oesophagitis research trial into biologics. Starting a new national study into AI in endoscopy. He has over 60 publications and over 115 abstracts to date. He attends European Gastroenterology meetings regularly as well as the British Society of Gastroenterology meeting. He is a member of the Oesophageal Stomach Cancer -NI for patients He is a core member on the oesophageal section committee of the British Society of Gastroenterology, current secretary. He is actively involved in teaching both local, national and international. Dr Mainie is an Honorary Lecturer for Queens University Belfast.