Leslie built a successful career over 45+ years in senior management roles in both the pharmaceutical and medical device industries, culminating in the successful turnaround of a pharmaceutical business.

He was elected EMIG Chairman in 2005 and has been instrumental in the metamorphosis of EMIG from being a business/networking group to the influential trade association it is today. In 2005, EMIG began with 17 Member Companies and has 300+ today, of which, 90% choose to be represented only by EMIG. Consequently, EMIG represents c. 50% of UK branded medicines.

In July 2014, Leslie was elected VP, European Confederation of Pharmaceutical Entrepreneurs (EUCOPE) and appointed to the Board of the EU Medical Cannabis Association in 2019. He was Vice Chairman of the NICE Project Development Group for Local Formularies Good Practice Guidance, a member of the NICE Medicines Optimisation Guidance Development Group and is currently an Expert Adviser to the NICE Centre for Clinical Practice.

He has been involved with the negotiation of the 2024 Voluntary Scheme and was a Member of the Working Group for the NICE Review of Methods and Process. He has published numerous articles, is a frequent speaker at national and international seminars, a Member of MENSA and is a visiting lecturer at the University of Cambridge.

In April 2020, Leslie became co-founder and Chairman of TetrisPharma Ltd.