Luke Miels will take over on Jan 1 from Walmsley, who will have been at the helm for almost nine years, GSK said in an unexpected announcement.
GSK earlier this month said it planned to invest US$30 billion in the US over the next five years.
The investment was announced before US President Donald Trump said last week that he would impose 100% tariffs on all branded pharmaceutical products from Wednesday, unless companies are building manufacturing plants in the US.
“2026 is a pivotal year for GSK to define its path for the decade ahead, and I believe the right moment for new leadership,” Walmsley said in the company’s statement.
“Today, GSK is a biopharma innovator, with far stronger momentum and prospects than nine years ago,” she added.
Miels, 50, said he will be leading a company “with outstanding prospects”.
“As the next CEO, I am privileged to take on this responsibility, with humility and ambition,” he added.
Following news of the appointment, GSK shares jumped 3.5%, topping London’s benchmark FTSE 100 index in early deals.
Covid, spin-off
Following their recent announcements to invest substantially in the US, GSK and its British rival AstraZeneca will be hoping for some kind of exemption, similar to that which the EU says it is set to gain thanks to a trade deal with the world’s biggest economy.
A former AstraZeneca executive, Miels’s annual base salary as CEO will be £1.375 million (US$1.85 million), below Walmsley’s current level.
However, he could earn millions more in yearly and long-term bonuses, the company statement noted.
Walmsley, who was also promoted from within as CEO, steered GSK through the Covid-19 pandemic and the separation of its consumer healthcare division.
The 56-year-old spun off the unit in 2022, later name Haleon, to concentrate on GSK’s main pharmaceutical business.
It came after Walmsley faced intense activist shareholder pressure over the company’s delays in producing Covid jabs and treatments.
More recently, she oversaw GSK agreeing to pay US$2.3 billion to end lawsuits alleging that its heartburn drug Zantac caused cancer, despite the group not admitting liability.
That hit its annual profit in 2024, with the group on course for an improved performance this year thanks to booming sales of cancer medicines.