Gov. Tim Walz of Minnesota offered himself as a bridge to disillusioned Americans who regard the Democratic Party as a bastion of coastal elitism, in a high-stakes address formally accepting the vice-presidential nomination on Wednesday night.

From the stage of the Democratic National Convention in Chicago, Mr. Walz completed his breathtaking transformation from little-known governor to leading party figure, accentuating his Midwestern roots and portraying the Democratic ticket as one that champions pragmatism and patriotism.

“We’re all here tonight for one beautiful, simple reason: We love this country,” he said.

A month ago, many Americans outside Minnesota were unfamiliar with Mr. Walz, other than highly engaged Democrats who delighted in his punchy television appearances and memorable critiques of Republicans, whom he labeled “weird.”

But on Wednesday, as he gave the most consequential speech of his career, attendees made clear they had quickly become familiar with his life story, including his background as a former high school football coach.

Before he took the stage, convention organizers handed out signs that read “Coach Walz,” and a burly group of his former players, now middle-aged, marched out to the tune of their high school fight song. Chants of “Coach” rang out during his speech, which was rife with football metaphors.

“It’s the fourth quarter. We’re down a field goal,” Mr. Walz said. “But we’re on offense and we’ve got the ball. We’re driving down the field. And boy, do we have the right team.”