The mortgage company Rocket is buying competitor Mr. Cooper in an all-stock deal valued at $9.4 billion, just weeks after acquiring real estate listing company Redfin.

Rocket Cos. said Monday that bringing Mr. Cooper Group Inc. into the fold will create a business representing one in every six mortgages in the United States. The deal will boost loan volumes, the company said, while lowering client acquisition costs.

Mr. Cooper shareholders will receive a fixed exchange ratio of 11 Rocket shares for each share of Mr. Cooper common stock.

Rocket shareholders will own approximately 75% of the combined company, while Mr. Cooper stockholders will own about 25%.