I'm thrilled to announce my running mate, @TimKaine, a man who's devoted his life to fighting for others. -H pic.twitter.com/lTVyfztE5Z

— Hillary Clinton (@HillaryClinton) July 23, 2016

TAMPA, Fla. — Hillary Clinton named Senator Tim Kaine of Virginia to be her running mate Friday, selecting a battleground-state politician with working-class roots and a fluency in Spanish, traits that she believes can bolster her chances to defeat Donald J. Trump in November.

Kaine, 58, a former Virginia governor, Richmond mayor and Democratic National Committee chairman, was chosen after a search that included riskier and more unconventional candidates who offered greater appeal to the party's liberal base.

He was a longtime favourite to become Clinton's running mate, however, in part because of the political and personal attributes she considers well-suited to the governing partnership she seeks - and in part because of the calculation that the experience of a Clinton-Kaine ticket would outgun Trump's outsider bombast.

Clinton notified supporters of her selection in a tweet.

"I'm thrilled to tell you this first," the tweet read. "I've chosen Sen. Tim Kaine as my running mate. Welcome him to my team.”

Kaine is not known for his charisma on the campaign trail; he has called himself the "happy senator" and even "boring" - and Clinton laughingly agreed in a PBS interview earlier this week.

"I love that about him," she said Monday.

"He's never lost an election. He was a world-class mayor, governor and senator, and is one of the most highly respected senators I know," she said.

Along with his image as a low-key workhorse, Kaine brings legislative experience in the Senate and executive experience as a popular if unremarkable governor. He comes from a battleground state, albeit one widely considered winnable for Clinton whether Kaine is on the ticket or not.

Clinton has said that her most important criterion was the ability to step into the presidency at any moment. She also sought a running mate who would be able to work with Republicans to advance an ambitious legislative agenda that includes immigration reform and new gun-control measures, her campaign said.

Kaine's affable, regular-guy presence may also help balance the perception of Clinton as remote, chilly and privileged. She is among the least-liked major party candidates in decades, according to public opinion polls, behind only Trump.

Trump selected Indiana Gov. Mike Pence as his running mate, a choice that added to the Republican ticket someone with experience and a resume with parallels to Kaine's.

Representing a state with a large military presence and defense industry has burnished Kaine's national security experience, and he serves on the Senate Armed Services Committee as well as the Foreign Relations Committee. He won admiration within the military and jolted Democrats when he pushed for congressional consideration of a new war authorization for the conflicts in Iraq and Syria. In 2015, he joined Sen. Jeff Flake, R-Arizona, to seek a new three-year authorization for military force. The effort stalled, but it raised Kaine's stature.