Trump announced the decision on Twitter on Friday after much media speculation over who the presumptive Republican presidential candidate would choose as a running mate.

The 57-year-old Pence is a relatively unknown figure outside of Republican circles and his own state, but is popular with the party's conservative base and leadership.

The six-term former congressman and governor of Indiana since 2013 has described himself as "a Christian, a conservative and a Republican, in that order."

Republican Party Chairman Reince Priebus said the decision offers a "very different style that I think shows a lot of maturity" on Trump's part.

By selecting Pence, Trump is trying to bring someone with political experience in Washington onto his team. He also hopes to attract conservatives and Republican Party members who have voiced reservations over the divisive and loose-tongued New York businessman.

Sabato's Crystall Ball, a political analysis blog run by the University of Virginia Center for Politics, said that while vice presidential picks rarely matter in presidential elections Pence could help overcome some of Trump's weaknesses.

"A social and economic conservative with strong religious views and think-tank credentials, Pence could conceivably shore up some of Trump's weaknesses among certain strands of the GOP base and some ideologically-committed conservatives inside and outside the Beltway," it said in an analysis of Pence; "Beltway" is a reference to the ring road around Washington D.C., but is used as shorthand for the federal government.

Pence brings what some Republicans consider a more traditional political hand to the campaign.

Paul Ryan, the speaker of the Republican controlled House, has sensitive relations with Trump but calls Pence a good friend.

"We need someone who is steady and secure in his principles, someone who can cut through the noise and make a compelling case for conservatism," Ryan said after the announcement.

Trump and Pence did not know each other that well until recently. The two have spent more time together over the past few days and campaigned. It is believed Pence was the first choice of Trump's children, who have strong influence over their father.

Still, Pence and Trump have differing views on a number key issues and it remains to be seen how the two will cooperate.

Trump has attacked free trade while Pence has been supportive of trade deals. The two also don't necessarily see eye-to-eye immigration. Pence has called Trump's call to ban Muslims from entering the US "offensive and unconstitutional," though he has tried to block Syrian refugees from coming to the United States.

Pence has tough views on abortion, gay rights and other socially conservative issues - all things that make him popular with the party base. His more discreet and calm character may help to balance out Trump's outbursts and unpredictability.

Hillary Clinton's campaign wasted no time calling him the "most extreme pick in a generation."

"By picking Mike Pence as his running mate, Donald Trump has doubled down on some of his most disturbing beliefs by choosing an incredibly divisive and unpopular running mate known for supporting discriminatory politics and failed economic policies that favor millionaires and corporations over working families," said John Podesta, Clinton's campaign chairman.

Trump was forced to make the vice presidential decision on Friday ahead of two deadlines. The Republican National Convention meets in Cleveland, Ohio, on Monday to formally nominate Trump as the party's candidate.

Pence also had to notify the state whether he would withdraw from the reelection campaign for governor of Indiana by noon on Friday. State law prohibits a candidate from running for two positions.

New Jersey Governor Chris Christie and former House Speaker Newt Gingrich were also on Trump's shortlist.

cw/msh (AFP, AP, dpa, Reuters)