Dr Dionne has held senior roles in the pharmaceutical industry, life science investment and life science academic sectors.
He replaces outgoing CEO Dr Mark Goldsmith, who will stay on as Executive Chairman.
Constellation discovers and develops small-molecule drugs for cancer and inflammatory/immune disorders based on epigenetics, the study of gene expression mechanisms beyond DNA.
Dr Dionne most recently served as entrepreneur-in-residence at life science investment firm Third Rock Ventures. His previous roles include CEO of Aurface Logix, CEO of Alantos Pharmaceuticals, and two VP roles (for R&D and technology) at Millennium Pharmaceuticals.
In his previous academic career, Dr Dionne was Adjunct Professor in the Biomedical Department at Brown University.
“With more than 20 years of experience leading US and international biotech companies, research and development teams and successful strategic alliances between companies, Keith is ideally suited to lead this phase of our organisation and advance our leadership in epigenetics drug discovery and development,” said Dr Goldsmith.
Dr Dionne commented: “I’m delighted to join Constellation at this exciting time in the company’s growth and evolution as we approach clinical milestones in our internal programmes and continue to realise the full potential of our platform in conjunction with our broad discovery alliance with Genentech.”