Microsoft Corp. MSFT -1.20% agreed to buy Activision Blizzard Inc. ATVI +28.11% in an all-cash deal valued at $68.7 billion, using its largest acquisition by far to grab a videogame heavyweight that has been roiled by claims of workplace misconduct.

The deal, if completed, would sharply expand Microsoft’s already sizable videogame operation, adding a stable of popular game franchises including Call of Duty, World of Warcraft and Candy Crush to Microsoft’s Xbox console business and its own games like Minecraft and Doom. Microsoft said the transaction would make it the world’s third-largest gaming company by revenue, behind China’s Tencent Holdings Ltd. and Japan’s Sony Group Corp.