The London-based pharmaceuticals giant said Yamada, 60, will retire June 1 to take up the role of executive director, Global Health Program, for the Bill & Melinda Gates Foundation.
Slaoui, 46, is Glaxo's senior vice president, worldwide business development and external alliances in R&D.
"Tachi has been a principal architect behind the transformation and dramatic improvement in GSK's R&D productivity, and he leaves GSK in a position of strength," said CEO Jean-Pierre Garnier. "We now have an impressive pipeline of innovative medicines that will benefit patients around the world and provide a strong platform for GSK's future prosperity.
"With his enormous experience and empathy for patients, Tachi will bring inspirational leadership to the Gates Foundation in its global quest for better health care. The Gates Foundation is a pivotal partner with GSK, and we look forward to continuing a strong relationship with Tachi in his new role.
"Moncef is a highly regarded scientist in industry and academia, and he has played a key role in the development of GSK's strong pipeline of vaccines and pharmaceutical medicines during his 17 years with the company. His expertise in new product development will enable him to lead GSK's R&D organization into a new era, as it delivers its exciting new pipeline."