Allen & Overy is promoting more than double the number of assistant solicitors to partners this year compared to 1999.
Next month, 40 new partners will be created. In May last year, only 17 were made up.
John Rink, managing partner at A&O, says the boost in numbers reflects the growth of the firm in the past year.
A&O acquired the Amsterdam and Luxembourg offices of Benelux firm Loeff Claeys Verbeke earlier this year, and the firm took over Madrid practice Satrustegui & Asociados in 1999.
A spokesman for A&O says that the impact of these acquisitions must be added to the firm's increased manpower from its mergers with Italian practice Brosio Casati e Associati and Bangkok firm MPS & Associates in 1998.
Its mergers in the past two years in Benelux, Madrid, Italy and Bangkok have added 316 fee earners to the firm.
Rink says: "A&O has grown substantially in the past year. It is automatic that the bigger you get, the more partners you will be making up.
"If a two-partner firm makes one partner it increases by 50 per cent, so if a 300 partner firm grows it will also [increase the number of partners proportionally].
"When I started as managing partner in 1994 we were about 500 fee earners. Now we are 1,630."
The firm's recent recruitment drive has also bulked out the practice. Over the past year, the number of fee earners in the firm has increased by a third.
Most of the new partners are in the UK office and specialise in banking, international capital markets or corporate law.