K&L Gates, the Pittsburgh-based law firm with one of the District’s most profitable lobby shops, plans to absorb Australian firm Middletons, creating one of the world’s largest law firms with more than 2,300 attorneys on five continents.

The combination, approved by partners at both firms Monday, will add to K&L Gates’ growing international reach by folding in Middletons’ 300 lawyers in four Australian offices under the K&L Gates brand. The merger is effective Jan. 1, and will boost K&L Gates’ presence in the Asia-Pacific region to 400 lawyers and 11 offices, including the recently announced office in Seoul that is slated to open in January.

Earlier this year, K&L Gates, which has about 235 lawyers in the District, absorbed the nine-lawyer Italian firm Marini Salsi Picciau Studio Legale.

K&L Gates chairman and global managing partner Peter Kalis will remain in the top post, and Middletons’ national managing partner Nick Nichola will become the Australia managing partner for K&L Gates.

In a joint statement, Kalis and Nichola said the combination will align the firm’s business with the businesses of clients in an era of globalization.

“With the largest integrated network of law offices and law partners of any global law firm, our clients will be able seamlessly and efficiently to access top-notch legal resources around the corner and around the world,” they said in the statement.

The combination is the second major merger involving a top U.S. law firm in less than a month. In November, SNR Denton announced it would merge with Canadian law firm Fraser Milner Casgrain and European firm Salans to form Dentons, a 2,500-lawyer firm. The merger was approved by partners last week.