"GSK plc today announced that Sir Andrew Witty, CEO, has indicated to the board his intention to retire from the company in early 2017," the London-listed group said in an unexpected announcement alongside its annual report.
Witty, 51, who has worked for GSK and in the pharmaceuticals industry for the last 32 years, will leave the group at the end of next March, it said.
GSK will now search for a successor and will consider internal and external candidates.
"In making this decision it has been important to me that the board have the time to conduct a full and proper process and that we sustain the momentum of our current business performance, capitalising on the very significant progress we made last year to strengthen the group."
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GSK chairman Philip Hampton paid tribute to the outgoing chief executive.
"Andrew's retirement next year will represent the culmination of 32 years of service and leadership to GSK and the industry," he said.