Kamala Harris has said she was "proud" to select Tim Walz as her running mate, opting for the Minnesota governor with blue-collar credentials as the partner most likely to boost her historic White House bid.
Mr Walz had been on a vice-presidential shortlist with a string of other Democratic figures seen as broadening Ms Harris's appeal as she sprints into the contest against Donald Trump.
Aiming to make history as the first woman US president, Ms Harris - already a trailblazer as the first female and first Black and South Asian vice president - has little time before Election Day on 5 November.
"I am proud to announce that I've asked Tim Walz to be my running mate," she posted on X.
"As a governor, a coach, a teacher, and a veteran, he's delivered for working families like his. It's great to have him on the team."
I am proud to announce that I've asked @Tim_Walz to be my running mate.
— Kamala Harris (@KamalaHarris) August 6, 2024
As a governor, a coach, a teacher, and a veteran, he's delivered for working families like his.
It's great to have him on the team.
Now let's get to work. Join us:https://t.co/W4AE2WlMTj
President Joe Biden quickly expressed support for his deputy's "great decision" to choose Mr Walz, saying the duo "will be a powerful voice for working people and America's great middle class."
Expectations had always been that Harris would pick a white man to balance the ticket and help win over working-class, white, male voters, a demographic that propelled Mr Trump to victory in 2016.
Mr Walz fits that description as a 60-year-old midwesterner with a folksy manner, decades of military experience and a rural perspective.
He dismisses the "nonsense" of Mr Trump and Republican running mate JD Vance, and he is also a gun-owner who tweets about hunting, goes ice-fishing and rides rollercoasters with his daughter.
The onetime teacher and school sports coach flipped a Republican district in 2006 to win a seat in the House of Representatives in a state seen as lightyears from the coastal elites of California, Ms Harris's home turf, or the east coast.
At the same time, Mr Walz will appeal to the left for championing cannabis legalisation, worker protections, abortion rights, and tighter firearm restrictions.
Tim Walz: teacher, veteran, governor - and now VP pick
Mr Trump's campaign branded the Minnesotan as a "dangerously liberal extremist" seeking to impose California values on the nation.
Democratic grandee Nancy Pelosi swatted such criticism aside, telling MSNBC that Mr Walz "is right down the middle. He's a heartland of America Democrat."
Mr Walz earned enthusiastic endorsements from Democratic liberals as well as centrists like Senator Joe Manchin, who called him "the real deal."
After being named by Ms Harris, he said it was the "honor of a lifetime" and quipped it felt like "the first day of school."
The pair will hit the campaign trail immediately, launching a five-day swing through battleground states starting in the biggest prize, Pennsylvania.
It has been a remarkable journey for Ms Harris, who only entered the race last month when 81-year-old Mr Biden withdrew, bowing to mounting concerns over his age.
The former prosecutor and senator has since obliterated fundraising records, attracted huge crowds and dominated social media on her way to erasing what had been Trump's growing lead in polls over Mr Biden.
The latest University of Massachusetts Amherst poll has Harris leading Trump nationally by three percentage points, 46 to 43, compared to a four-point lead for Mr Trump over Mr Biden in January.
In the swing states that decide US elections, Ms Harris is neck and neck with Mr Trump, who shocked the world with his 2016 victory but was beaten by Mr Biden in 2020.
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Picking a running mate was seen as the first big test for Ms Harris.
Now, she and Mr Walz will face the first hurdle of their ground game as they head from Pennsylvania to Wisconsin, Michigan, Arizona and Nevada.
Pennsylvania is part of the "blue wall" that carried Mr Biden to victory in 2020 - one reason many had expected Ms Harris to pick state governor, Josh Shapiro.
Mr Vance, speaking to supporters in Philadelphia, said her refusal to pick Mr Shapiro, who is Jewish, as her running mate showed she "listened to the Hamas wing of the party."
Harris-Walz campaign co-chair Mitch Landrieu shot back, telling CNN that Ms Harris "reiterates our support for Israel" and that Mr Walz "has done the same."
Mr Trump was riding high last month after surviving an assassination attempt at a rally, and then using the Republican convention to highlight his image of vigor against the physically frail Mr Biden.
But with Mr Biden's exit and Ms Harris's fast start, he is scrambling to recalibrate.
At a rally Saturday, Mr Trump called Ms Harris a "Marxist" who would cause an "economic crash."
