Great Portland Estates has confirmed the let of One Rathbone Square, W1 to Facebook.
The social media giant will take all the 227,324 sq ft of space in the development on a 15-year lease without break.
The company will occupy the site from its predicted completion date of February 2017, paying an initial rent of £16.9m.
Facebook has also signed an agreement with Great Portland Estates to lease a further 15,461 sq ft in the building, subject to it achieving planning permission for a change of use from retail to office.
GPE will also extend first offer rights to Facebook on offices at 73/89 Oxford Street which are due for completion in April 2017.
A similar agreement exists for space at Oxford House, 76 Oxford Street, W1 co-terminus with Rathbone Square and 73/89 Oxford Street.
