Kim is of Korean descent. Kim grew up in Ridgewood, New Jersey the son of a single mother, and his first job was in 1974 at a Roy Rogers restaurant, where he earned money to pay for college. Kim earned his A.B. in chemistry at Cornell University in 1979 where he conducted research with the late George P. Hess. He received his Ph.D. in Biochemistry at Stanford University under the guidance of Robert L. (“Buzz”) Baldwin.

Kim joined Merck Research Laboratories (MRL) in 2001 as executive vice president, Research and Development. He was promoted to president in January 2003. In this role Kim oversaw all of Merck’s drug and vaccine research and development activities.

During his tenure, Merck gained approval of more than 20 new medicines and vaccines. These include Januvia (the first DPP-4 inhibitor for type 2 diabetes), Gardasil (the first vaccine for prevention of cervical cancer), Isentress (the first HIV integrase inhibitor), Zostavax (the first vaccine for the prevention of shingles in adults), and Rotateq (an oral vaccine for the prevention of rotavirus infection in infants). He also led the biomarker-based development of Keytruda. In 2013, he retired from Merck and was succeeded by Roger Perlmutter. He was appointed to the faculty at Stanford University in 2014.