The studio was one of the many that Activision Blizzard hoped to sell after the Vivendi Games merger, with Swordfish's 50 Cent game among those dropped from the company's publishing slate as it did not fit with Activision's sequel-centric plans.
Monumental picked up Swordfish's 26-person Manchester branch for an undisclosed sum. The fate of the Birmingham office is not yet known, though publisher THQ has signed on to release 50 Cent: Blood on the Sand early next year.
"The Swordfish team is one of the very few developers worldwide to have fully solved the hugely complex issues involved in running and managing the XLSP (Xbox Live! Server Platform) server environments for online console gaming," explained Monumental CEO Rik Alexander.
"This knowledge base will help to consolidate Monumental's position as the market leading online game developer."