Tim Walz introduced himself to millions of Americans on a star-studded night at the Democratic National Convention Wednesday, as he accepted the nomination to be Kamala Harris's 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."

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."

The relatively unknown state-level official brings a Midwestern everyman vibe to Harris's 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's 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.

'Fight for your freedom'

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's speech and the climax of a convention that has defied predictions of 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," he said.

On Tuesday, it was Democratic superstars Michelle and former president Barack Obama who spoke, following up on Biden's emotional speech Monday, where he passed the torch to his vice president.

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

He 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."

As a folksy, white son of the US heartland, Walz balances Harris's California background and barrier-breaking status as the first Black woman nominee.

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 -- a remarkable turn of events, given that 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 and rising Democratic star Josh Shapiro to former president Bill Clinton.

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