Valentin spent 17 years in the CNS Drug Discovery Department at the Bristol-Myers Squibb Pharmaceutical Research Institute in Wallingford, Connecticut, where he founded and was the head of the Ion Channels Drug Discovery Group and head of the Circadian Rhythm laboratory. He was Co-Chair of several drug discovery working groups, including the Ischemic Stroke Working Group.

He left BMS in 2004 to be the Vice President of Ion Channel Biology at Scion Pharmaceuticals in Medford Massachusetts, which we sold to Wyeth Pharmaceuticals in 2006. He was recruited to lead the biology effort at Knopp Neurosciences (now Knopp Biosciences) in Pittsburgh, Pennsylvania in 2006, where he was the Chief Scientific Officer in charge of their ALS program.

He left Knopp in 2013 to take a position as Head of Research at Elan Pharmaceuticals, which was sold later that year. He is currently an Associate Professor (Adj.) at Yale Medical School, where he conducts basic research into mechanisms of bioenergetics regulation of neuronal function and the mechanisms of neonatal genetically-linked epilepsies. He is also a consultant to several biopharmaceutical companies in the Cambridge, Massachusetts area and in London, United Kingdom