GlaxoSmithKline has appointed Emma Walmsley, its current head of consumer healthcare, as its new chief executive.
Ms Walmsley, who joined the UK's biggest drugmaker in 2010 from L'Oreal, will replace current chief Sir Andrew Witty in March 2017.
Ms Walmsley describes herself as "extremely competitive" with "a bit of a bias for action".
She will be the firm's first female chief executive, and one of only seven female FTSE 100 chief executives.
She spent 17 years at French cosmetics firm L'Oreal, where she worked in the UK, Europe, the US and China in marketing and management.
Ms Walmsley joined GlaxoSmithKline in 2010, and became a member of the executive team in 2011, running the division selling products including toothpaste, headache tablets and the malted barley drink, Horlicks.
The firm produces a broad spectrum of medical and consumer products from prescription medicines, vaccines and HIV treatments to skincare products.
'Delighted and honoured'
Big firms have come under increasing pressure to change a culture where women can find it difficult to get into the boardroom.
Between 2012 and 2014, nearly three quarters of FTSE 100 companies had no female executives at all on their boards.
And data suggests that the gender pay gap widens after women return to work after their first baby.
Ms Warmsley, who is married with four children, will become chief executive of by far the biggest firm in the FTSE 100 with a woman at the top.
Analysis: Simon Jack, BBC Business editor
Emma Walmsley will become one of the most powerful business figures in the UK when she takes over as chief executive of GSK in March of next year.
The pharmaceutical giant is the fourth most valuable public company in Britain with 100,000 employs around the world, 16,000 of them here.
GSK has changed dramatically under her predecessor Sir Andrew Witty, with Ms Walmsley an important agent in that change.
After working at L'Oreal for 17 years, she was hired in 2010 in to boost the consumer products division which sells brands like Sensodyne and Panadol and now makes up nearly a quarter of the company's revenues.
This diversification was a key strategy of the outgoing Sir Andrew Witty who believed it would mitigate the risks involved in drug development.
It was not without its critics, with many investors arguing the company would be worth more split into separate businesses.
After a bumpy few years punctuated by poor financial performance and drug mis-selling scandals in the US and China, GSK has recently hit a more confident stride.
Its shares have risen 20% over the last year and it recently invested £275m in expanding its UK manufacturing facilities.
In a statement, Ms Walmsley said: "I am delighted and honoured to be appointed GSK's next CEO.
"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."
Sir Andrew has been with GSK for more than three decades, having started as a management trainee.
During his nearly ten years as boss, Sir Andrew has overseen initiatives such as the firm's plan to drop patents in the world's poorest countries.
The firm has been developing what could be the world's first malaria vaccine as part of a thirty-year project.
As well as Horlicks, GlaxoSmithKline's consumer healthcare business includes brands such as Aquafresh toothpaste and Tums indigestion tablets.
Ms Walmsley's appointment could be seen as a signal that GSK will keep its consumer operation as a core part of its business.
"Under Andrew's leadership, GSK has successfully developed into a company with market-leading positions in pharmaceuticals, vaccines and consumer healthcare," chairman Philip Hampton said.
"These provide excellent platforms for sustainable, long-term growth, and we are confident Emma will successfully build on these strengths."
GlaxoSmithKline employs around 16,000 people in the UK, with about 6,000 of those employed in manufacturing.