Active in the Senate in foreign relations and military affairs, the 58-year old Kaine has a reputation for working with both parties as Virginia's governor and Richmond's mayor.

The Spanish-speaking moderate senator is from one of the key battleground states, Virginia, and is seen as giving Democrats the edge there.

Clinton described Kaine as "a man who's devoted his life to fighting for others." She called him "a relentless optimist who believes no problem is unsolvable if you put in the work to solve it."

Other candidates for the post included Agriculture Secretary Tom Vilsack and Massachusetts Senator Elizabeth Warren.

Clinton's pick comes a day after Donald Trump was officially named as the Republicans' presidential candidate in the upcoming November election, amid demonization of Clinton and chants of "lock her up" at the party convention in Cleveland.

Trump wasted little time in attacking Kaine after the nomination.

Clinton earlier Friday called the Republican convention "perversely flattering."

"I never thought I'd say these words but Ted Cruz was right," Clinton said at a campaign rally in Tampa. "In this election, do the right thing and vote your conscience." Cruz pointedly refused to endorse Trump on Thursday.

The Democratic convention in Philadelphia starts on Monday.

jbh/cmk (AP, Reuters)