Emma Walmsley, who was previously GlaxoSmithKline’s consumer healthcare boss, will replace Sir Andrew Witty when he retires next March.
Walmsley has been appointed chief executive designate and will join a small band of women at the top of the UK's biggest listed companies when she takes on the post.
She has headed Glaxo's £6bn consumer healthcare arm since it was created in March 2015 as part of a joint venture deal with Novartis.
Walmsley joined Glaxo in 2010 from L'Oreal, where she held a variety of marketing and general management roles in the UK, Europe and United States over a 17-year career at the group.
She said: "I am delighted and honoured to be appointed GSK's next chief executive.
"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."
Sir Andrew announced plans to retire on 31 March 2017 earlier this year, ending nearly nine years at the helm and more than three decades with Britain's biggest drugs company.
Sir Philip Hampton, chairman of Glaxo, said Walmsley's appointment follows a "very thorough and rigorous" selection process.
He added: "Emma is an outstanding leader with highly valuable experience of building and running major global businesses and a strong track record of delivering growth and driving performance in healthcare."
Walmsley has been a member of Glaxo's corporate executive team since 2011 and will join its board of directors from January.
Glaxo said Walmsley's salary is yet to be announced, with Glaxo soon to begin talks with shareholders as part of an overhaul of executive pay.
Her base salary will be announced on 1 January, while her total pay package will be set out in the group's annual report next spring.
It comes as executive pay is in the spotlight at the group after it was disclosed that Sir Andrew's total pay surged by 71% to £6.7m last year, despite falling core earnings and sales.
He was paid a salary of just under £1.1m for 2015, while he was also handed an annual bonus payment of £2.2m and long-term share awards worth £2.6m, although 25% of his annual bonus is deferred.