Prior to joining Vertex Pharmaceuticals Inc, Dr. Leiden has been Managing Director of Clarus Ventures since 2007. Dr. Leiden joined Clarus Ventures in November 1, 2006 as a Partner. Dr. Leiden has more than 20 years of experience in the biomedical and pharmaceutical sectors.
He served as President and Chief operating officer at Abbott Laboratories in 2001. Dr. Leiden served as an Executive Vice President, Pharmaceuticals and Chief Scientific Officer from 2000 to 2001 at Abbott Laboratories. 
During his academic career, he was involved in starting several Biotechnology companies including Vical and Cardiogene Therapeutics Inc.
From 1987 to 2000, Dr. Leiden served several academic appointments including the Chief of Cardiology and Director of the Cardiovascular Research Institute at the University of Chicago at University of Chicago School of Medicine. 
From 1992 to July 1999, Dr. Leiden was the Frederick H. Rawson Professor of Medicine and Pathology. Dr. Leiden has been Chairman of the Board of directors of VBI Vaccines. Dr. Leiden served as Chairman of the Board of directors of Lycera Corp. Dr. Leiden served as Chairman of the Board of directors of TYRX, Inc. (formerly TyRx Pharma, Inc.) since February 28, 2008. 
He serves as Director of Catabasis Pharmaceuticals. He has been a Director of Abbott Laboratories since 1999. Dr. Leiden has been a Director of Vertex Pharmaceuticals Incorporated, since July 7, 2009.
He served as a Non-Executive Director of the Board of Shire Plc from January 1, 2007 to January 31, 2012. He served as a Director of TYRX, Inc. since February 2008. He served as Member of the Scientific Advisory Board at Massachusetts Life Sciences Center until September 30, 2011. 
Dr. Leiden serves as a Member of the Board of Trustees of the Ravinia Festival, the Museum of Science and Industry, the Keystone Symposia, and the Penn Medicine Board of the University of Pennsylvania. He also serves as the Chairman at the University of Pennsylvania, School of Medicine. 
Dr. Leiden serves as a Member of the American Society for Clinical Investigation and the Association of American Physicians. In 2001, he was elected a fellow of the American Academy of Arts and Sciences and Member of the Institute of Medicine of the National Academy of Sciences. During his 14 year career in academia, Dr. Leiden published more than 130 peer reviewed papers.
Dr. Leiden earned both, an M.D. and a Ph.D. from the University of Chicago. He has also received an honorary M.A. from Harvard University. Dr. Leiden earned a Bachelor's degree in Biological sciences from the University of Chicago.