More than 2,300 people will work for Facebook in the country by the end of 2018, according to a statement.
The 7-floor building, located at Rathbone Place, near Oxford Circus in central London, is designed by Frank Gehry, the world-renowned architect of the Guggenheim Museum in Bilbao and the Walt Disney Concert Hall in L.A.
Teams of engineers, developers, marketing and sales will work there.
"Today's announcements show that Facebook is more committed than ever to the UK and in supporting the growth of the country's innovative start-ups," Nicola Mendelsohn, Facebook's Vice President for Europe, Middle East and Asia, said.
The office will also house an incubator space for start-ups called LDN_LAB.
UK-based start-ups could take part in three-month long programmes to help them "kick start and accelerate their businesses."
Facebook opened its first office in London ten years ago.
“It is great to see a world-leading company like Facebook continuing to invest in London’s renowned tech ecosystem, despite the uncertainties surrounding Brexit," Julian David, CEO of techUK said. TechUK is a collective which represents more than 950 companies employing 700,000 people in the UK.
"Facebook has chosen to be amongst like-minded businesses and the brightest minds in placing its very first in-house start-up incubator, LDN_LAB, in the UK," added David.