UK firm Dibb Lupton Broomhead has struck a formal association with 355-lawyer Chicago practice Hinshaw & Culbertson.
Both firms say the partnership will aim to share expertise for mutual client benefit, refer business to each other, participate in joint projects and regularly second lawyers to each others firms.
Thomas Hamilton, partner in charge of Hinshaws insurance coverage practice, said: "For each firm, we found ourselves trying to serve clients with foreign needs in separate jurisdictions without the consistency that could be provided by a formal association.
"In talking with our clients, we confirmed that almost all of them have a London legal requirement that could be met, had we had a sister firm."
Dibbs found its clients wanted transactional and litigation expertise in the US as well as support work for foreign ventures.
Dibbs managing partner Paul Rhodes said: "In our search for a firm with a strong presence in the midwestern portion of the US, we found the perfect match.
"I am confident that our aggressive styles and similar firm philosophies will form the basis of a long and successful relationship."
Hinshaws has offices in Chicago and 16 others throughout Illinois, Wisconsin and Florida.
Beyond the benefit to clients, each firm is likely to draw upon a strength in its less well-known areas of practice. Hinshaws, a top insurance defence firm, is likely to gain in its lesser-known corporate area. Dibbs will gain in its non-corporate law areas.
Formal merger is not on the cards. Hamilton said: "A British lawyer is most effective in Britain and a US lawyer is most effective in the US. I believe each should stay where they are most effective but then learn from each others competencies to serve clients better."
The learning process is scheduled to begin when each firm hosts a senior partner from each other's practice for a period of two to three months.
As the first lawyer in this exchange, Hamilton said he would be coming to London this month to talk with Dibbs lawyers about uniquely US issues of interest, such as tort reform, products liability and products recall.
He will familiarise himself with all Dibbs' practice groups, offices and clients, as well as meeting with Hinshaw clients located in London and any Dibbs clients with US legal needs. Following Hamilton's visit, a Dibbs senior partner will arrive in Chicago this summer and from then on the two firms will begin formal exchanges of junior lawyers.
While both Hinshaw and Dibbs are optimistic about the long-term prospects of the association, some Chicago lawyers remain sceptical of the arrangement.
Jerry Homsy, senior partner with Chicago-based litigation firm Zevnik, Horton, Guirbord & McGovern, whose six offices include a formal one in London, said: "In these associations, everyone wants to have the other firm's clients referred to them.
"In a diffuse sort of way, with a non-specific pledge of association, you lose your focus on the fact that most clients like to pick their own lawyer in their own jurisdictions."