SNR Denton is preparing to merge with Canadian law firm Fraser Milner Casgrain and European firm Salans by early next year, the firms announced.

The merger, which is to go before partners at all three firms for a vote by Nov. 30, would create one of the world’s largest law firms, with 2,500 attorneys and professionals in 52 countries. The new firm would be called Dentons.

It is the second major merger in less than three years for SNR Denton, which was formed in 2010 when Chicago-based Sonnenschein Nath & Rosenthal combined with UK firm Denton Wilde Sapte. SNR Denton has about 130 lawyers and professionals in Washington, where the firm’s chief executive, Elliott Portnoy, and chairman, Joe Andrew, are based. Portnoy and Andrew would remain in their leadership positions.

Worldwide, SNR Denton has about 1,200 lawyers and professionals; Salans, founded in Paris with offices throughout Europe, has 830 attorneys. FMC has 520 lawyers in six offices in Canada.

Although the demand for legal services has remained largely flat since 2009, mergers continue to be a common growth strategy for law firms — 16 law firm mergers were announced in the third quarter alone, according to legal consulting group Atman Weil, which tracks law firm mergers and acquisitions. But the “bigger is better” strategy comes with risks: it’s costly to absorb additional real estate responsibilities, client conflicts often arise, and integrating different partner pay systems can breed internal discontent and take years to smooth out.

Portnoy said all three firms have merit-based compensation systems that will be aligned over a two-year period.

“Time will tell if buying the Roman Empire plus Canada is worth it,” said Ivan Adler, a headhunter for lawyers and lobbyists at The McCormick Group. “Their merger mania has worked so far.”

Portnoy said the merger is expected to close in the first quarter of 2013. It would create the largest energy, mining and resources practice at any law firm — boosting SNR Denton’s existing energy practice in Washington, which handles transactional, litigation and regulatory work for companies in the energy sector.

Dentons is not going to have a global headquarters and is not seeking to create a dominant national culture. Portnoy and Andrew say that is because the purchasers of legal services are increasingly international, and are looking for legal talent more than geographic ties.