Minneapolis' oldest continuing law firm Gray Plant Mooty will merge with Kansas City, Mo., firm Lathrop Gage.

The merger, which will take effect at the beginning of next year, will combine nearly 400 attorneys and 14 offices across nine states to form Lathrop GPM LLP, according to a Thursday announcement.

"Both of our firms are, first and foremost, dedicated to our clients, and this combination will provide them with expanded services to meet their growing needs," said Gray Plant Mooty Managing Officer Michael Sullivan Jr., in a statement. "The synergies between Gray Plant Mooty and Lathrop Gage are remarkable. Together we will have the expertise in a wide range of practice areas and geographies to better serve our clients."

Gray Plant Mooty's current Minneapolis office in the downtown IDS Center, which employs 118 lawyers, will remain open along with the firm's offices in St. Cloud, Fargo, N.D., and Washington, D.C. Sullivan will serve as the partner-in-charge of the new firm's Minneapolis office, as well as a member of the executive committee responsible for integration efforts.

Gray Plant Mooty, with origins dating to 1866, employs 155 attorneys in its combined offices. It is known for its franchise and distribution law practice that helps franchisers in all stages of business development as well as its health law, higher education, mergers and acquisitions and nonprofit practices.

Founded in 1873, Lathrop Gage, which has 240 attorneys across the country, provides guidance in litigation, business and intellectual property law among other practice areas.

"Clients are at the heart of everything we do," said Lathrop Gage Managing Partner Cameron Garrison, in a statement. "Our work helps them seize opportunities, solve problems and dominate their marketplace. This combination offers Lathrop Gage clients experienced attorneys in new legal practices and access to deeper benches in several areas."

Law firms in the Twin Cities as well as across the country have continued to consolidate to better compete against larger firms and expand their services. Last year, there were 106 law-firm combinations in the United States, the highest annual total recorded in more than a decade, according to Altman Weil MergerLine, which tracks law-firm mergers.

Minneapolis-based Briggs and Morgan in August said it had agreed to merge with Taft Stettinius & Hollister, a Midwest law firm with offices in Indianapolis, Chicago and Cincinnati. The deal will create a firm with about 600 attorneys and takes effect Jan. 1.

Nicole Norfleet • 612-673-4495 Twitter: @nicolenorfleet