"I am pleased to announce that I have chosen Governor Mike Pence as my Vice Presidential running mate. News conference tomorrow at 11:00 A.M.," the presumptive Republican nominee tweeted.
They will hold their first joint event Saturday morning, currently planned for New York Hilton Midtown in Manhattan, CNN has learned, after earlier plans to have an event in New Jersey.
Pence is in New York meeting with senior advisers, the source said. Trump had originally planned to announce his running mate at an event Friday, but Trump postponed his announcement citing the deadly terror attacks in Nice, France.
A Trump campaign adviser said Trump was frustrated with all of the reports confirming that Pence was the pick while the businessman was in California on a fundraising trip, "six hours and three time zones away no less."
CNN reported Thursday
that Trump offered Pence the vice presidential slot, and that Pence accepted it. Later, however, Trump told Fox News and told host Greta van Susteren, "I haven't made my final, final decision," doing his best to keep the drama going after a frenetic day.
Trump's campaign chairman Paul Manafort told CNN's "New Day" Friday that Trump's final decision on his running mate isn't final "until he announces it," but he added that the real estate mogul will "honor his word" to whomever he picked.
Manafort fanned speculation saying that despite reports -- including CNN's -- that Trump has picked Pence, "until he announces it, it's not final."
He added, though, that "Donald Trump, whoever he selects, and whomever he says is the selection, will honor his word. That's who he is." Manafort said that he expects the announcement to be made over the weekend.
Manafort's comments Friday came during an extended interview with CNN's Chris Cuomo where he said the reason he had delayed the announcement was because the campaign thought it would be inappropriate to hold a political event so soon after the terror attacks in Nice, France on Thursday.
"The postponement is because of what happened in France yesterday was so tragic. It bothered him to see that carnage and felt the pain of the people there. It's just not right to do something self-serving and political the morning after," Manafort said. "So he said I want to postpone it."
Cuomo pressed Manafort on why Trump was continuing to play coy about the pick -- despite reporting that Pence was offered the position, and accepted it.
"Until he announces it, it's not final. That's true. He announced a change because it had nothing do with politics, today, he'll be announcing when he makes the decision. I expect there will be an announcement of his choice before we get to Cleveland," Manafort said.