President Biden used his valedictory address at the Democratic National Convention on Monday to deliver a lengthy defense of his own record aimed at cementing a 50-year legacy of public service, even as he passed the reins to Vice President Kamala Harris as the new face of the party he led until just weeks ago.

Speaking to a raucous arena filled with Democrats who chanted “We Love Joe!” and gave him a three-and-a-half-minute standing ovation, Mr. Biden grew emotional as he delivered what amounted to a political farewell to his most fervent supporters.

“I’ve given my heart and soul to our nation, and I’ve been blessed a million times in return,” the president said as he made the case that Ms. Harris is the best person to lead the country now that he is no longer in the race.

“She’s tough. She’s experienced. And she has enormous integrity,” Mr. Biden said. Selecting Ms. Harris as his vice president, he added, “was the best decision I made my whole career.”

That was not the case that Mr. Biden expected to be making just over a month ago, before his stunning political demise following a debate performance that raised doubts about his age and vitality. And in some ways, his praise of Ms. Harris during the 52-minute address seemed secondary to his desire to recount the greatest hits of his career in a speech he might have given as the party’s nominee.

One by one, Mr. Biden ticked through a litany of achievements from the stump speeches of his now-ended campaign: $35 insulin; breathing room for American families; strengthening NATO; beating “big Pharma”; burn pits that harmed veterans; investments in infrastructure; appointing a Black woman to serve on the Supreme Court; and the now-familiar call to remember “who the hell we are: We’re the United States of America, and there’s nothing we can’t do if we do it together.”