Sources familiar with campaign operations cautioned that while Pence and Gingrich were finalists, Trump could always have a last-minute change of heart and choose someone else from his short list.
Gingrich on Thursday outlined what he called an arduous vetting process with Trump's campaign, which included 113 detailed questions and a request for everything he had written.
He told reporters Thursday: "I hope that he picks a good movement conservative".
The 22-member panel would have 30 days to select a new nominee for governor, but former state Republican Chairman Mike McDaniel said he expects a decision will be sooner.
Rokita and Brooks, as well as supporters of Holcomb, have contacted the state Republican committee, said two of its members, Nick Barbknecht and Barbara Krisher.
In an interview with Fox News Channel's "The O'Reilly Factor", Trump says, "This is war". Trump said following Pence's introduction. Clinton says she would intensify efforts to put together a more effective coalition against terrorism.
The other leading contenders for the Republican running mate are New Jersey Gov. Chris Christie and former Speaker of the House Newt Gingrich.
Trump spent Tuesday and Wednesday in IN with Pence after a campaign rally in Westfield. Indianapolis television station WTHR posted a video showing Pence arriving Thursday evening at a private airport outside NY.
But as governor of the Hoosier state, Pence may present a credibility to voters in Midwestern states other candidates on Trump's shortlist were missing, Lenkowsky said.
With the ticket now full and the Republican National Convention beginning next week, the eyes of the nation will now be upon the Trump/Pence ticket.
Republican presidential candidate Donald Trump will announce Indiana Gov. Mike Pence as his running mate, multiple sources have reported.
"Pence really balances out the ticket and offers more of a wide base of appeal than Trump has just by himself", Albright said. But some of Trump's children, who have been closely advising their father, are said to favor different candidates.
As the day began, it appeared the decision would come quickly.
Influential figures within Trump's staff were said to be urging the real estate mogul to pick Pence, whose record of conservative governance could soothe Republicans wary of Trump's unconventional proposals and inexperience in Washington policy-making.
Gingrich suggests that he has yet to hear from Trump about his decision.
The presumptive Republican presidential nominee tweeted on Wednesday night that he would announce his choice on Friday at 11 a.m. (1500 GMT) in Manhattan.
Ms Ginsburg, the 83-year-old senior liberal member of the high court, inserted herself into the USA presidential election in recent days by making negative remarks about Mr Trump in a series of media interviews. His campaign chairman, Paul Manafort, is now in Cleveland, and none of his children are in the state with him.
In the past 24 hours, after Trump and Pence very publicly met at the Governor's Mansion, reports have ignited more talk. He cannot run for both re-election as governor and for vice president, and he must withdraw by noon Friday so that the state party can replace him on the ballot.