In its first merger outside the US, White & Case has joined forces with Brussels-based European law boutique Forrester Norall & Sutton.
The five lawyers currently stationed at White & Case's office in the Belgian capital will move into Forrester Norall's premises when the merger takes effect on 1 January.
The combined office, with 23 lawyers, gives the US firm one of the largest teams of any of the foreign firms in the city.
Both firms had been looking at ways of consolidating their positions in the highly competitive Brussels market.
James Hurlock, chairman of White & Case's management committee, said that what to do in Brussels had been a "constant question" since the firm set up there almost 20 years ago.
Like many foreign firms in the city, the office kept only a handful of lawyers busy doing a mix of regulatory and corporate work.
But over the last few years, the feeling grew that the EU side of the practice needed to be developed as Brussels' role as a regulator of business increased.
Hurlock added: "We have long felt that we wanted to develop a litigation capability to handle trade and competition matters as well as other EU matters."
Forrester Norall faced different problems. It was set up 17 years ago when there were few foreign firms in Brussels and, like other boutique firms such as Van Bael & Bellis and Stanbrook & Hooper, was a pioneer in giving advice on European law to multinationals.
That changed at the beginning of the 1990s when foreign firms descended on Brussels in droves.
Partner Christopher Norall said: "Some of the arguments for being a boutique have gone. Ten years ago, we had a lot of referral work, but this has diminished".
He said that the firm "seriously considered staying as a boutique" but felt its future lay in providing European law advice within the framework of a global network.
The firm's eight partners, which include UK, Greek and US-qualified lawyers, join White & Case as partners.