Live updates: Harris and Walz take the stage in 1st joint campaign rally

Gov. Tim Walz posted on X on Tuesday, saying he's "all in" on his new role as Harris' VP pick.

"It is the honor of a lifetime to join [Kamala Harris] in this campaign. I'm all in. Vice President Harris is showing us the politics of what's possible. It reminds me a bit of the first day of school. So, let's get this done, folks! Join us," he wrote, also linking to a donation page.

Kamala Harris has officially announced Gov. Tim Walz as her vice presidential running mate.

"I'm pleased to share that I've made my decision: Minnesota Governor Tim Walz will join our campaign as my running mate," Kamala Harris wrote in a text sent to supporters on Tuesday.

"Tim is a battle-tested leader who has an incredible track record of getting things done for Minnesota families. I know that he will bring that same principled leadership to our campaign, and to the office of the vice president."

"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," she posted on X.

Rep. Betty McCollum, D-Minn., praised Gov. Tim Walz on Tuesday, calling him a "rock-solid Democrat."

"Tim Walz is my friend and a former colleague whose Midwest values are rooted in selfless service to our nation, caring for his neighbors, and inspiring students, soldiers and citizens to stand together, dream bigger and never give up," she said in a statement, reacting to the news that Vice President Kamala Harris is poised to pick the Minnesota governor as her running mate.

"Tim is a rock-solid Democrat, a teacher, a football coach, a veteran and a leader who will defend our freedoms and will work to improve the lives of all Americans in every corner of our country," she said.

-ABC News' John Parkinson

Former House Speaker Nancy Pelosi reacted to the news that Vice President Kamala Harris will pick Minnesota Governor Tim Walz as her running mate on Morning Joe, saying "Tim Walz is wonderful, and she had many good choices among the six and among the two."

"Tim Walz, I know very well. He served in the House. To characterize him as left is so unreal. It's just not - he's right down the middle. He is a heartland of America Democrat. He was the chair of our veterans affairs committee, and I don't want anybody to forget that - he made tremendous, tremendous gains for our veterans," Pelosi said.