This woman just became the most powerful female CEO in the FTSE 100
Walsmley joined Britain's biggest drugs company from L'Oreal in 2010, and is currently head of GSK's consumer healthcare division. She will take over from Andrew Witty when he retires in March next year.
Walmsley joins just six other female chief executives in the FTSE 100. Easyjet, Imperial Brands, Royal Mail and Kingfisher are run by women.
GSK's market value is nearly £80 billion ($105 billion). That is nearly double that of the next largest female-led company, the tobacco company Imperial Brands, whose value is £38 billion ($50 billion).
Philip Hampton, GSK chairman, said the selection process for the new chief executive had been "very thorough and rigorous."
"Emma is an outstanding leader with highly valuable experience of building and running major global businesses," he added.
Hampton is currently chairing an independent review into increasing the number of female executives at Britain's biggest companies.
Walmsley said: "I am delighted and honoured to be appointed GSK's next CEO. GSK is a company that leads both in science and in the way it does business.
"We have momentum in the group and as the demand for medical innovation and trusted healthcare products continues to rise, we have the opportunity and the potential to create meaningful benefits for patients, consumers and our shareholders.
"I'm looking forward to working with Andrew and other leaders over the next few months to ensure a smooth handover and to develop plans for 2017 and beyond."