Harris officially names Tim Walz as vice presidential running mate

Vice President Kamala Harris has officially named Minnesota Gov. Tim Walz as her vice presidential running mate to help her challenge Donald Trump and JD Vance in November.

The Harris campaign sent out an official announcement on Tuesday morning, saying that Walz and Harris will "crisscross" the country to present a split-screen on who is "running to move the country forward" and who is running to move the country "backward." Harris and Walz are set to visit seven battleground states this week -- beginning with a rally together on Tuesday evening in Philadelphia. Vance is set to visit the battleground states this week as well.

The campaign highlighted Walz's background as a Midwesterner and a gun owner who "believes that Congress must do more to tackle gun violence in our communities."

Walz posted on X on Tuesday that he's "all in" on his new role as Harris' vice presidential pick.

"It is the honor of a lifetime to join @kamalaharris in this campaign," Walz wrote. "I’m all in."

Walz, 60, made a name for himself in the veepstakes as he gained major traction online with his folksy mannerisms and viral comments calling Trump and Vance "weird."

He served in the Army National Guard and was a high school social studies teacher and football coach before he was elected to Congress in 2006.

He won six terms in the U.S. House representing a rural area of the state that had typically leaned conservative.

Why pick Walz?

Harris likes Walz's executive experience and a his "strong record of accomplishment for middle class families that models what we want to do nationally," according to a source close to the selection process. Specifically, a Harris-Walz campaign will highlight his fight for expanded child tax credits, junk-fee ban, paid-leave policies, gun safety legislation and codifying Roe v. wade protection, the source said.

As governor, he's implemented a bevy of progressive policies, including paid family leave, universal school breakfast and lunch, legalization of recreational marijuana use, state codification of abortion rights and gun control measures like universal background checks and red flag laws.

Harris and her campaign love his bio, the source told ABC News, adding that it "will appeal in key Midwest states we must win." As a veteran, football coach, hunter and gun owner, Walz has a "deep connection to rural American," the source added.

Also, Walz has a record of winning in a Trump-voting district as a House member.

Harris' team loves the "weird" line he came up with in his attacks against Trump and Vance -- and think that it's a line that will stick against their opponents, the source said.

And this person cites a "strong personal rapport and confidence in his ability to be a governing partner" as a key reason Harris made the selection.

Harris told Walz that they are the underdogs

Harris told Walz in a phone call Tuesday morning that they are the underdogs in this race -- but that she’s confident that together they have a winning message on reducing costs for the middle class and protecting freedom, according to a source close to the process.

President Joe Biden spoke separately to Harris and Walz Tuesday morning, according to the White House. Biden spoke with the vice president before she announced Walz would be her running mate and also "spoke with Gov. Walz to congratulate him on his selection," White House Senior Deputy Press Secretary Emilie Simons said in a statement.

The source said that chemistry was a big piece of Harris’ decision to choose Walz.

Harris notified her team Tuesday morning that she wanted to inform Walz and the other candidates of her decision, the source said. The final decision and execution was done this morning, the source added.

Campaign chair Jen O’Malley Dillon and Liz Allen, the chief of staff to Harris' running mate, are currently briefing Walz and the teams ahead of their rally Tuesday night in Philadelphia.

Walz as a Harris surrogate

As a surrogate for Harris these past few weeks, Walz has praised her for reenergizing Democrats and defended her record against Trump's attacks claiming she is "ultra-liberal."

"He's going to roll it out, mispronounce names, you know, to try and make the case," Walz said of Trump attacking Harris during a recent appearance on CNN. "The fact of the matter is where you see the policies that Vice President Harris was a part of making, Democratic governors across the country executed those policies and quality of life is higher, the economies are better, all of those things, educational attainment is better."

This is a developing story. Please check back for updates.

ABC News' Gabriella Abdul-Hakim, Brittany Shepherd, Justin Gomez and Sarah Beth Hensley contributed to this report.