Leary spent most of her clinical and analyst career in cancer, and worked with the National Cancer Action Team from 2005 to its dissolution in 2013 as part of the Lansley reforms. She was subsequently appointed a Chair in Healthcare and Workforce Modelling at the London South Bank University in 2014. She is interested in the complexity of healthcare and ways to use non-linear mathematics to model hospital staffing and outcomes. She has argued that the healthcare workforce should be evaluated based on outcomes, rather than outputs. This could be achieved through improving staff working conditions and pay, as well as streamlining immigration processes for shortage occupations. Leary believes that better planning could greatly improve the healthcare system, focussing on better understanding demand and risk. She has questioned the protection of the job title of nurse, emphasising that it is important to use it only for the highly trained specialists within the National Health Service. She has supported the idea of bringing more men into nursing to mitigate for the staff shortfall, but could exacerbate current equality issues within the nursing profession. Leary studied the gender pay gap in nursing, and found that male nurses reached higher paying posts more quickly and were overrepresented at higher pay grades. In 2016 she was awarded a Winston Churchill Memorial Trust Fellowship to study the use of big data in high reliability organisations. This position allowed her to compare healthcare with other safety critical industries in Switzerland and the United States of America. Leary serves as the clinical lead at Millwall Football Club. In this capacity she helps the football club deploy emergency healthcare, and studies what roles are required for the most effective response team. Her research on the effectiveness of medical teams is part of Millwall F.C.'s new approach to healthcare services, which can accommodate disasters as well as minor injuries, spectator safety and primary care. This work was included in the Sports Safety Ground Authority's 2018 guide, which sets benchmarking standards in British football grounds. She is a member of the TED Whitehall Women expert group. She has served as non-executive director of several charities, including the National Lung Cancer Forum for Nurses and the Millwall Community Scheme.
