Sidley & Austin is moving to new offices at 1 Threadneedle Street this week, in the expectation of doubling its number of fee earners over the next five years.
Since setting up the London operation in 1994, the office has grown to 45 fee earners including 10 partners - but the firm says further organic growth and lateral hires are expected.
Last year Sidley & Austin poached several partners, including Mark Pinder from Travers Smith Braithwaite, but also suffered setbacks, losing a number of assistants including senior corporate assistant Andrew Forryan, who went to Clifford Chance.
The new office, just round the corner from the current office in the Royal Exchange Building, is said by Sidley & Austin partner Drew Scott to be "not as nice a looking a building" but "functional" and much bigger.
John Edwards, managing partner of the London office, said: "We have been severely restricted for space in the last year, so it is with enormous relief that we are moving to larger premises."