Two of Missouri’s biggest law firms have agreed to merge, creating a 630-lawyer powerhouse that will rank among the top 100 in the country in size and revenue.

Partners at Kansas City-based Blackwell Sanders and St. Louis-based Husch & Eppenberger approved the combination over the weekend. The electronic vote in favor of the union was nearly unanimous, according to Blackwell Chairman David Fenley.

“The whole notion of achieving a great deal more depth and more expertise is very attractive to clients and to people who may become our clients,” he said.

The merger is expected to close in January. A name for the combined firm has yet to be chosen.

Blackwell has about 330 attorneys and grossed $116.5 million in 2006, according to The American Lawyer, a legal publication. About half the firm’s attorneys are based in the Kansas City area.

Husch, which has a 40-attorney office in downtown Kansas City, has about 300 attorneys overall. The firm tallied $124 million in revenues in 2006.

The firms said they expected to generate combined revenues in 2008 of more than $275 million.

The marriage of the two firms dwarfs any previous law firm combination in Missouri, creating the state’s second-biggest legal shop. The biggest firm headquartered in Missouri is St. Louis-based Bryan Cave, which has about 800 attorneys.

“This will really differentiate them from other firms in the market,” said Lisa Smith of Hildebrandt International, a provider of consulting services to law firms. “And it gives them the platform to expand regionally.”

Smith, who advised Blackwell and Husch on the merger, said the union would give the new firm the kind of beefed-up resources that clients are increasingly demanding.

“Clients aren’t looking for size so much as practice depth,” she said. “This gives them additional depth in all of their practices. It really combines complementary practices because the relative strengths of each firm are a little different.”

Blackwell is best known for its corporate, transactional, real estate, and labor and employment practices. Husch is best known for its litigation, commercial finance, environmental and bankruptcy practices.

The last major cross-state merger of law firms took place 3 ½ years ago when Kansas City-based Polsinelli Shalton & Welte merged with St. Louis-based Suelthaus PC, creating a 190-lawyer firm with 70 lawyers in St. Louis. The firm, now called Polsinelli Shalton Flanigan Suelthaus, currently has close to 300 attorneys.

The biggest law firm merger in Kansas City occurred more than five years ago when two of the city’s largest and oldest firms — Stinson Mag & Fizzell and Morrison & Hecker — combined to create a 342-lawyer practice. That firm is now known as Stinson Morrison Hecker.

The union of Blackwell and Husch will give the combined firm 16 locations in Missouri, Kansas, Nebraska, Illinois, Tennessee, Washington, D.C., and London. The firms have overlapping offices in three cities — Kansas City, St. Louis and Springfield.

Fenley said the merged firm will address lease issues in those cities “as soon as we can, but we’re going to accomplish physical integration irrespective of having two offices in the same cities.”

Blackwell has 13 years remaining on its lease in the Plaza Colonnade, located at Main Street and Ward Parkway overlooking the Country Club Plaza. The firm moved in three years ago and occupies about 120,000 square feet on four floors. Husch occupies three floors downtown at 1200 Main St. and has nine years to run on its lease.