Little-known outside of the Midwest just four weeks ago, Governor Walz will take centerstage at the Democratic National Convention tonight — a remarkable rise for a man who was not considered a shortlister for Vice President Harris’s running mate until he impressed her with his communication skills and relatable life story. 

Mr. Walz, a 60-year-old father of two, won the plaudits of many liberals just in the past 18 months after his party took control of the Minnesota state legislature, which allowed it to invest more money in green energy, provide for paid family leave, legalize marijuana, pass stronger union protections, and — most famously — provide free meals for Minnesota students. 

His branding of President Trump and Senator Vance as “weird” immediately caught on for Democrats who were reinvigorated after Ms. Harris took the helm. Across the country, the vice president and her running mate have been rallying with tens of thousands of people who are finally excited about the election. 

Congressman Dean Phillips, himself a Minnesotan who launched a quixotic primary challenge against President Biden this year, says his home state governor is exactly who Ms. Harris needed to help her win the presidency. Mr. Phillips says Mr. Walz — a native son of rural Nebraska and transplant to rural southern Minnesota — helps Democrats speak to those white, working-class voters that the party has lost in droves to Trump. 

“Right now … based on what I’m feeling, sensing — both in my district, in this room, around the country — I think the tables are turning,” he said. “I think she is going to win primarily because she selected a guy who I think can finally speak to voters in a part of the country.”

Mr. Walz’s biography had been a key selling point for Ms. Harris, who has touted both her upbringing and her running mate’s as the perfect encapsulation of the American story — two people of different races and different genders, born into the middle class in different parts of the country, who ended up rising to the highest level of American politics. With Mr. Walz’s history as a National Guardsman, a teacher, a coach, and red-district congressman, Ms. Harris felt that he could help sell her vision in the heartland. 

One problem with being relatively unknown, though, is the risk of national media descending on one’s life story. Republicans have made an issue out of Mr. Walz embellishing aspects of his personal story, including his description of himself as a command sergeant major in the Minnesota National Guard and his claim that he is a veteran of Operation Enduring Freedom, which may have left some to believe that he served in combat in Afghanistan. 

The truth, though, was that the Minnesota governor never completed the commander sergeant major training program, so he actually retired one rank lower as a master sergeant. He is technically a veteran of Operation Enduring Freedom as well, though he deployed to Italy in a support role for a number of months with his unit. 

So far, Ms. Harris’s bet on Mr. Walz appears to be paying off despite the controversies. On the night Ms. Harris introduced Mr. Walz to the nation as “Coach Walz” during a rally at Philadelphia, her husband, Doug Emhoff, seemed thrilled after the governor’s rousing speech. “You made the right choice,” Mr. Emhoff could be seen saying to the vice president when he walked out on stage with Gwen Walz. “I know,” Ms. Harris replied with a smile. 

Unlike Mr. Vance, Mr. Walz has many more fans than detractors if polling is to be believed. According to a survey from the Associated Press released on Wednesday, Mr. Walz has a net positive approval rating of 11 points, with 36 percent of voters having a positive view of him while 25 percent have a negative view. Mr. Vance on the other hand has a net negative rating of 17 points, with 44 percent disapproving of the Ohio senator and 27 percent having a positive view of him. 

President Obama, like many other Democrats, seemed thrilled with the choice of Mr. Walz for VP. “Let me tell you something — I love this guy,” the former president said in his speech to delegates on Tuesday night. “Tim is the kind of person who should be in politics — born in a small town, served his country, taught kids, coached football, took care of his neighbors. He knows who he is and he knows what’s important.”