Mrs Obama, who has spent nearly eight years in the White House avoiding political fights, took numerous swipes at Mr Trump, while avoiding mentioning him by name.
Michelle Obama has electrified the Democratic Convention in Philadelphia, imploring the party of her husband to “knock on every door” to ensure Hillary Clinton is the next American president.
With an intensity of passion the country had not seen before, the first lady delivered a primetime address driving home her commitment to supporting Ms Clinton while offering pointed digs at her Republican foe, Donald Trump, despite never once mentioning his name.
“Don’t let anyone tell you this country isn’t great,” Ms Obama declared, thrilling a sports arena in Philadelphia that was packed to capacity on the convention’s first night.
“That somehow we need to make it great again. Because this right now is the greatest country on earth.“
In a speech that emphasised children, including her own daughters, Ms Obama offered the most poignant evidence of the progress America has made when she noted the history of black Americans who “felt the lash of bondage” and the “sting of segregation”.
“I wake up every day in a house that was built by slaves,” she declared before reflecting that now she can look out and “watch my daughters, two intelligent black young women, play with their dog on the White House lawn.”
Raising the volume in a speech that won a rapturous reception, Ms Obama exhorted Democrats to work as hard as they can to deny Republicans victory in November. It was a case being made by a serving first lady on behalf, of course, of someone who had held that position before her.
It was also a case, however, made by a wife, who eight years ago had invested all her emotions in blocking the rise of that same Ms Clinton who threatened her own husband’s rise and bid for the White House. But that was then. And between then and now, they have often worked together.
“Hear me,” she cried, “between now and November we need to do what we did eight years ago and four years ago. We need to knock on every door, we need get out every vote, we need outpour every last ounce of our passion and strength” to make sure Ms Clinton is president.
“I want someone with the proven strength to persevere, someone who knows this job and takes it seriously, someone who understands the issues a president faces are not black and white,“ said Ms Obama. Referring to Mr Trump's penchant for practising politics by the medium of Twitter, she said of the presidency: "It cannot be boiled down to 140 characters.“
With former Bill Clinton in the hall to cheer her on, Ms Obama was clearly emotional as she spelled out her admiration for the former first lady - who on Thursday will be on the stage herself to accept the Democratic nomination - and highlighting the contrasts between her and Mr Trump.
Once a reluctant participant in the political sphere, the first lady has grown into a potent cultural icon in America, a journey that recently included her appearance as guest on carpool karaoke segment made popular by the British comedian and now late-night TV host, James Corden, singing - or rocking - with Mr Corden and, in the last minutes, Missy Elliott.
But on Monday night in Philadelphia she also showed a new willingness to engage directly in the political drama that the 2016 election has become, driven clearly by her own alarm at the nature of the man challenging Ms Clinton.
“When you have the nuclear codes at you fingertips and military at your command, you can’t make snap decisions,” she said. “You can’t have thin skin or a tendency to lash out. You need to be steady and well-informed. I want a president with a record of public service, someone who’s life work shows our children we don’t chase fame and fortune for ourselves.”
“She has made all of us proud,” Senator Bernie Sanders said of Ms Obama at the start of his own speech that came later and triggered an even greater festival of frenzy in the hall. Her husband, Barack Obama, expressed his pride in a Tweet. “Incredible speech by an incredible woman,” he said.
"Best speech of the night," the former Governor of Pennsylvania, Ed Rendell, who is also chairman of the Convention Host Committee, told The Independent as he left a sky box when the gavel was dropped ending the night's session.
This presidential election “is about who will have the power to shape our children for the next four or eight years of our lives,” Ms Obama said, “and I am here tonight because in this election there is only person I trust with that responsibility.that is our friend, Hillary Clinton.”
“Because of Hillary Clinton, my daughters take for granted that a woman can be president of the United States,” she added.