Donald Trump has introduced Indiana Governor Mike Pence as his running mate, completing the Republican ticket for the presidential election.
At a Manhattan hotel, the New York property developer said his vice-presidential pick was a "solid" man.
He tried to dispel reports that he had been conflicted about his choice by insisting the 57-year-old governor was definitely his first choice.
Mr Pence is well known for his strong socially-conservative credentials.
The governor joined Mr Trump on stage and described him as "a good man" who "will make a great president".
Mr Trump will be formally made the Republican presidential candidate at the party's national convention in Cleveland this week.
Mr Trump praised his vice-presidential choice as man who had served "with distinction" in Congress equipped with "the skills of a highly talented executive".
"I introduce a man who I truly believe will be outstanding in every way and who will be the next vice-president of the United States, Governor Mike Pence," he said.
Trump takes centre stage - Jane O'Brien, BBC News, Washington
Introducing a vice-presidential candidate to the nation is usually a well-choreographed affair. But the first joint appearance between Donald Trump and his new running mate seemed almost an afterthought.
Mr Trump spoke for more than 30 minutes - mainly about himself while taking sideswipes at Hilary Clinton - leaving Mike Pence quite literally waiting in the wings.
When he did get round to talking about the man he hopes will boost his popularity among wavering Republicans, Mr Trump resorted to his notes, praising Mr Pence's track record as a congressman and governor of Indiana and describing him as a "solid, solid person".
By contrast, Mr Pence gave a far more conventional speech, sticking to his script and delivering a measured message of support for Donald Trump.
It was hard to gauge what, if any, personal relationship exists. The two shook hands briefly, greeted each other's families and left the stage. Mr Trump appeared relieved to have got the formalities out of the way while Mr Pence gave little sign of emotion.
Joining Mr Trump on the podium, Mr Pence said: "I come to this moment deeply humbled but with a grateful heart, grateful to God for his amazing grace."
He said his new boss was someone who understood the frustrations of ordinary Americans in a way reminiscent of former President Ronald Reagan.
Quoting the former president, who is still a hero to many Republicans, he said: "We're tired of being told that a little intellectual elite in a far distant capital can plan our lives better for us."
And abroad, Mr Trump would be a strong leader who would stand with America's allies and "destroy the enemies of our freedom", Mr Pence said.
The two men have their differences on policy - Mr Pence is a supporter of trade deals opposed by Mr Trump, and the governor was critical of the proposed ban on Muslims coming to the US.
Mr Trump was not his first choice as nominee either. Mr Pence backed Texas Senator Ted Cruz.
Their joint appearance on Friday was rescheduled after the lorry attack in France, amid reports that Mr Trump only settled on Mr Pence after being talked out of other options by his family.
New Jersey Governor Chris Christie and former House Speaker Newt Gingrich were in the frame.