Shortly following the meeting, Trump tweeted the details of the agreement and said the deal never would have been done if "we (Trump) not won the election."
Trump and Masayoshi came down from his office in Trump Tower to announce the move to reporters gathered in the lobby of Trump Tower. Trump called Masayoshi "one of the great men of industry" before leaving the Softbank CEO to talk to reporters.
"I just came to celebrate his new job," Son said, according to a pool report. "I said, 'This is great, the US will become great again."
Softbank is the second-largest telecom by market share in Japan after rival NTT.
The Softbank move comes just a week after Trump announced a deal with United Technologies to keep 1,100 jobs at its Carrier plant in Indiana.
Following the news, shares of US-based telecom Sprint spiked up just over 2.3% as of 2:35 p.m. ET. Softbank owns 83% of Sprint.
Watch Trump and Masayoshi's announcement below:
BREAKING: Pres.-elect Trump makes surprise visit in Trump Tower lobby, says Softbank will invest $50B into the US to create 50,000 new jobs pic.twitter.com/tMY3fdBdxC