Democratic presidential candidate Hillary Clinton has selected Tim Kaine, a moderate senator from Virginia, as her running mate.
Mrs Clinton broke the news in a text message to her supporters, with a formal announcement planned for Saturday.
Mrs Clinton passed over more left-leaning candidates in favour of the 58-year-old senator, who opposes abortion and supports free-trade agreements.
His home state of Virginia is a major battleground in the coming election.
Groups against the Trans Pacific Partnership trade deal were dismayed at Mr Kaine's selection becaus of his support for a fast-tracking authority for the White House to negotiate the deal.
Critics of the trade pact, including Republican nominee Donald Trump and Mrs Clinton's Democratic primary rival Bernie Sanders, have said it would be unfair to US workers and kill jobs.
Mrs Clinton praised the TPP deal when she was secretary of state, but has since distanced herself from it.
She said Mr Kaine had relentless optimism, which was a much-needed attribute in an election season that was dark because of Mr Trump.
She also praised him as a man who had devoted his life to fighting for others.
Progressive Change Campaign Committee, which campaigned for such things as expanding Social Security benefits and Wall Street reform, said the issue gave Republicans a new opening to attack Democrats.
Who is Tim Kaine?
Mr Kaine also speaks fluent Spanish and could help the Clinton campaign maintain its support among Hispanic Americans - a growing voting bloc.
An experienced politician who has never lost an election and been toughly vetted, he is considered a "safe" choice for the vice-president slot.
He personally opposes abortion but supports abortion rights.
Mr Kaine was a finalist to be Barack Obama's running mate in 2008 and served as Virginia governor before his time in the Senate.
Mrs Clinton also reportedly interviewed liberal firebrand Senator Elizabeth Warren of Massachusetts and Senator Cory Booker, an African-American senator from New Jersey.