Ballard Spahr offices in Washington, D.C. March 24, 2015. Photo by Diego M. Radzinschi/THE NATIONAL LAW JOURNAL. Diego M. Radzinschi

Ballard Spahr is combining with Minneapolis-based Lindquist & Vennum, the two firms announced Tuesday.

The combined firm will operate under the name Ballard Spahr, and will have more than 650 lawyers across 15 offices. The deal makes Ballard Spahr one of the five largest Philadelphia-based law firms by head count, according to The National Law Journal’s rankings of the largest U.S. law firms.

Lindquist & Vennum, which has about 150 lawyers, focuses on corporate M&A, finance and litigation matters, working largely with middle-market companies. The firm has offices in Minneapolis, Denver and Sioux Falls, South Dakota.

For Ballard Spahr, the merger adds two offices and expands the firm’s longtime presence in Denver. The Minneapolis office will be Ballard Spahr’s largest outside Philadelphia.

But geography wasn’t a driving factor in the combination, Ballard Spahr chairman Mark Stewart said Tuesday.

“We have for some time been committed to deepening our business and finance practice,” Stewart said. “This offers us a very deep, well-known and highly regarded mergers and acquisitions and private equity group.”

The firm’s growth in its litigation practice has outpaced growth in its business practices, Stewart said, but after the recession, Ballard Spahr was looking to capitalize on increased dealmaking activity.

“Our litigation department has been on a pretty long and good run,” he said. “But we want to have some balance.”

Lindquist & Vennum managing partner Dennis O’Malley will now be part of Ballard Spahr’s executive team, Stewart said, and a partner from Lindquist & Vennum will also join the compensation committee. In the one market where both firms are present, Denver, the Lindquist & Vennum lawyers will move into Ballard Spahr’s existing office.

O’Malley said Lindquist & Vennum had been “courted” by a number of firms. It had pursued a merger with another legacy Minneapolis firm, Oppenheimer Wolff & Donnelly, but the two firms called off those discussions in early 2015, citing conflicts. Oppenheimer went on to be acquired by Fox Rothschild in December 2015.

Stewart said Ballard Spahr learned that Lindquist & Vennum was seeking a merger partner after the Oppenheimer deal fell apart. Talks between Ballard Spahr and Lindquist went on for almost a year, he said.

“We are excited to join a forward-thinking firm like Ballard, whose attorneys share our view that client relationships are strategic partnerships,” O’Malley said in a statement.

The two firms share few clients, Stewart said. There was one notable conflict between Ballard Spahr’s financial clients and a part of Lindquist & Vennum’s financial restructuring practice that focused on Chapter 7 trusteeships, he said. The conflicted lawyers are starting their own practice in Denver, Stewart said.

The deal was not necessarily seen as a surprise to competitors in Minneapolis. As Lindquist dealt with a string of partner departures that numbered more than 20 last year, one Twin Cities-based managing partner told Law.com last August that the firm was likely pursuing a major change.

“I think they have to be evaluating their strategic alternatives very seriously,” the managing partner said at the time. “But that was also true of Oppenheimer, and they held together for years under difficult circumstances.”

Ballard Spahr’s last merger was in 2013, when it acquired Stillman & Friedman, a white-collar and securities litigation boutique. The combination only added 14 lawyers, but allowed Ballard Spahr to enter the New York market.

In addition to its new offices and lawyers, Ballard Spahr is inheriting Lindquist & Vennum’s annual poetry prize, a $10,000 award it presents annually in partnership with nonprofit publisher Milkweed Editions. Stewart said he intends to continue the firm’s involvement in the contest.

Roy Strom contributed to this report.