BRUSSELS—Europe’s antitrust regulator plans to file formal charges against Google Inc. for violating antitrust laws, a person familiar with the matter said Tuesday, stepping up a five-year investigation likely to become the biggest competition battle here since the European Union’s pursuit of Microsoft Corp. a decade ago.

EU antitrust chief Margrethe Vestager made the decision Tuesday in agreement with European Commission President Jean-Claude Juncker, this person said. She is expected to inform her fellow EU commissioners...