PG&E Corp. filed for bankruptcy protection on Tuesday as it struggles with billions of dollars in potential liabilities from its role in sparking California wildfires, triggering one of the largest corporate-reorganization cases in years.

California’s biggest utility, which provides natural gas and electric service to 16 million people, sought protection under chapter 11 of the bankruptcy code. The process to restructure its debts is expected to be protracted, involving state and federal regulators, with wide-ranging...