By the end of next year about 2,300 people will work for the social media company in the UK.
The office will be Facebook's biggest engineering hub outside the US, and opens during its tenth year in the UK.
Nicola Mendelsohn, Facebook's Europe, Middle East and Asia vice-president, said the company was "more committed than ever to the UK".
She said Britain's "entrepreneurial ecosystem and engineering excellence" made it an ideal location for technology firms.
The seven-floor building at Rathbone Place, near Oxford Circus in central London, was designed by Frank Gehry, the architect best known for the Guggenheim Museum in Bilbao.
It will accommodate engineers and developers as well as marketing and sales teams.
The building will also house a dedicated incubator space for start-ups, called LDN-LAB.
UK-based start-ups will be invited to take part in three month programmes designed to help kickstart their businesses.
Facebook experts from disciplines including engineering, product and partnerships will work with the companies as part of the initiative.
Julian David of techUK, which represents 950 technology firms in the UK, welcomed a world-leading company such as Facebook investing in London despite the uncertainties surrounding Brexit.
Chancellor Philip Hammond said Facebook's decision to expand in London was a "sign of confidence" in Britain.
"The UK is not only the best place to start a new business, it's also the best place to grow one," he added.
Photo copyright: PA