The tech giant moved into the facility on Monday and will make it its biggest engineering hub outside of the United States as well as the home of its first incubator space for startups, LDN-LAB.
Built close to Oxford Circus, the HQ will also house marketing and sales teams, with Facebook's employee number in the UK set to reach a total of 2,300 by the end of 2018.
"The UK’s flourishing entrepreneurial ecosystem and international reputation for engineering excellence makes it one of the best places in the world to build a tech company," said Facebook's EMEA vice president Nicola Mendelsohn.
"And we’ve built our company here - this country has been a huge part of Facebook’s story over the past decade, and I look forward to continuing our work to achieve our mission of bringing the world closer together."
Concerns over Brexit have led to a number of billion-dollar companies such as Goldman Sachs hinting at moves away from the United Kingdom, but technology firms are staying loyal, with Google also set to construct a new London headquarters in King's Cross next year.