Masayoshi Son, the brash billionaire who controls Sprint Corp., said Tuesday he would invest $50 billion in the U.S. and create 50,000 new jobs, following a 45-minute private meeting with President-elect Donald Trump.

The telecom mogul, who made his fortune in Japan with SoftBank GroupCorp., announced his investment plans in the lobby of Trump Tower, though he didn’t provide details. Mr. Trump took credit for the investment, saying his November victory spurred SoftBank’s decision.

Mr....