Chicago Illinois - Tim Walz introduced himself to millions of Americans on Wednesday night at the Democratic National Convention, as he accepted the nomination to be Kamala Harris' White House running mate.

In a whirlwind quarter-hour address, Walz raced through the story of his middle-class upbringing in small town Nebraska, where he worked on the family farm, and described his experience teaching students who inspired him to go into politics.

"They saw in me what I had hoped to instill in them: a commitment to the common good, an understanding that we're all in this together, and the belief that a single person can make a real difference for their neighbors," he said as the crowd chanted "Coach Walz!"

The gloves came off as the 60-year-old Minnesota governor turned his fire on Republican nominee Donald Trump, accusing him of spending "all day insulting people and blaming others."

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But Walz devoted much of his speech at the United Center in Chicago to making the case for Harris.

"From her day as a prosecutor, as a district attorney, as an attorney general, as a United States senator and then our vice president, she's fought on the side of the American people," he said.

"She's taken on the predators and fraudsters. She's taken down the transnational gangs... She has never hesitated to reach across that aisle if it meant improving your lives, and she's always done it with energy, with passion, and with joy."

Walz brings a Midwestern everyman vibe to Harris' surging campaign against Trump that was central to his speech.

Introduced by Minnesota first lady Gwen Walz, the former National Guard soldier was cheered boisterously as he took to the stage for the biggest speech of his political career, ahead of Harris' big night Thursday.

In a moment that brought the audience to its feet, former students marched onstage to introduce Walz – a football coach in his teaching days – after a musical interlude by Grammy Award-winning musician John Legend.

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A surprise appearance by Oprah Winfrey and a rousing rendition of Higher Ground by Stevie Wonder made for a glitzy night, alongside turns from comic actors Mindy Kaling and Keenan Thompson.

Walz's main job was to tee up Harris' speech and the climax of a convention that has defied predictions of internal disunity or even chaos in the wake of President Joe Biden's decision to drop his reelection bid on July 21.

"No matter who you are, Kamala Harris is going to stand up and fight for your freedom to live the life that you want to lead, because that's what we want for ourselves and it's what we want for our neighbors," Walz said.

On Tuesday, former First Lady Michelle Obama and former President Barack Obama spoke in support of Harris, following up on Biden's farewell speech Monday, where he passed the torch to his vice president.

The convention has seen intense enthusiasm from supporters, buoyed by Walz's appearances at sideline events, where he has been mobbed by fans seeking selfies and chanting, "Tim! Tim! Tim!"

The vice-presidential candidate's events have also been targeted by Gaza solidarity protesters demanding a ceasefire and an arms embargo on Israel to protect Palestinians from US-backed siege, calls that have been amplified by thousands of people in the streets outside the convention. The Harris campaign has said she opposes a block on weapons transfers.

On the campaign trail, Walz has made a name for himself as an able communicator and is credited with coming up with one of the sharpest attack lines on Trump and his running mate J.D. Vance, whom he labeled "weird."

The chemistry between 59-year-old Harris and Walz and the noisy energy generated at their rallies is fueling Democratic hopes that they can defeat Trump (78) in November.

Polls show the election remains close, but Harris is moving slightly ahead. Only a month ago, Trump seemed to be gaining a steadily tightening grip on the race.

On the convention floor, delegates praised Walz's keynote address.

"I thought his speech was perfect," New York delegate Edwina Martin (60) told AFP. "I heard him at rallies say a lot of the same things, but tonight, hearing it in this setting was incredibly powerful and meaningful and inspiring."

Before Walz lit up the arena, the crowd heard from a galaxy of the party's biggest names, from Pennsylvania Governor Josh Shapiro to former President Bill Clinton.

"In 2024, we have a clear choice: 'We The People' versus 'Me, Myself, and I,'" Clinton said.