Vice president Kamala Harris has selected Minnesota governor Tim Walz to be her running mate on Tuesday, choosing a long-time politician who Democrats hope can keep new-found party unity alive.

Ms Harris said in a post on social media that Mr Walz has “delivered for working families”. The two will appear together in Philadelphia at an evening rally.

In choosing the 60-year-old, Ms Harris is turning to a mid-western governor, military veteran and union supporter who helped enact an ambitious Democratic agenda for his state, including sweeping protections for abortion rights and generous aid to families.

He is joining Ms Harris during one of the most turbulent periods in modern American politics, promising an unpredictable campaign ahead.

Republicans have rallied around former president Donald Trump after his attempted assassination in July.

Just weeks later, President Joe Biden ended his re-election campaign, forcing Ms Harris to unify Democrats and consider potential running mates over a breakneck two-week stretch.

Ms Harris hopes to shore up her campaign’s standing across the upper mid-west, a critical region in presidential politics that often serves as a buffer for Democrats seeking the White House.

The party remains haunted by Mr Trump’s wins in Michigan and Wisconsin in 2016.

Mr Trump lost those states in 2020 but has zeroed in on them as he aims to return to the presidency this year, and is expanding his focus to Minnesota.

Ms Harris, second gentleman Doug Emhoff and Mr Walz are set to appear together for an evening rally in Philadelphia, recalling a joint 2020 appearance by Mr Biden and Ms Harris in Wilmington, Delaware.

After Tuesday’s trip to Pennsylvania, they will spend the next five days flying thousands of miles around the country touring critical battleground states.

They will visit Eau Claire, Wisconsin, and Detroit on Wednesday, and Phoenix and Las Vegas later in the week.

Planned stops in Savannah, Georgia, and Raleigh-Durham, North Carolina, were postponed because of Tropical Storm Debby ’s effects.

A team of lawyers and political operatives led by former attorney general Eric Holder pored over documents and conducted interviews with potential selections, and Ms Harris herself met with her three finalists on Sunday.

She mulled the decision over on Monday with top aides at the vice president’s residence in Washington and finalised it on Tuesday morning.

Ms Harris, the first black woman and person of South Asian descent to lead a major party ticket, initially considered nearly a dozen candidates before zeroing in on a handful of serious contenders, all of whom were white men. In landing on Mr Walz, she sided with a low-key partner who has proved himself as a champion for Democratic causes.

Karoline Leavitt, Mr Trump’s campaign press secretary, said: “It’s no surprise that San Francisco liberal Kamala Harris wants West Coast wannabe Tim Walz as her running-mate – Walz has spent his governorship trying to reshape Minnesota in the image of the Golden State.

“Walz is obsessed with spreading California’s dangerously liberal agenda far and wide.”

Mr Walz has been a strong public advocate for Ms Harris in her campaign against Mr Trump and senator JD Vance of Ohio, labelling the Republicans “just weird” in an interview last month.

During a fundraiser for Ms Harris on Monday in Minneapolis, Mr Walz said: “It wasn’t a slur to call these guys weird. It was an observation.”

Mr Walz, who grew up in the small town of West Point, Nebraska, was a social studies teacher, football coach and union member at Mankato West High School in Minnesota before he got into politics.

He won the first of six terms in Congress in 2006 from a mostly rural southern Minnesota district, and used the office to champion veterans’ issues.

He served 24 years in the Army National Guard, rising to command sergeant major, one of the highest enlisted ranks in the military.

He ran for governor in 2018 on the theme of “One Minnesota” and won by more than 11 points.