Delivering the keynote speech later, Michelle Obama told the assembly that her husband represented typical American values.
She said: "What struck me when I first met Barack was that even though he had this funny name, and even though he'd grown up all the way across the continent in Hawaii, his family was so much like mine."
"He was raised by grandparents who were working class folks just like my parents, and by a single mother who struggled to pay the bills just like we did."
Michelle Obama's comments came as a rejection of Republican accusations that Barack Obama is an aloof celebrity.
She has faced similar attacks during the presidential campaign, with Republican accusations of her being unpatriotic when she said her husband's political success made her proud to be an American for the first time in her adult life.
Part of Michelle Obama's task in Monday's speech was to soften her own image as an assertive black woman - an image some American voters feel uncomfortable with.
"I come here as a wife who loves my husband and believes he will be an extraordinary president," she told the audience. "I come here as a mom whose girls are the heart of my heart and the center of my world."
Barack Obama, campaigning in Iowa, also made an appearance via video screen as his two daughters crowded onto the Denver stage with his wife.
Obama promised his much-hyped nomination acceptance address to the convention on Thursday - the 45th anniversary of Martin Luther King Jr's "I Have a Dream" speech -would be "workmanlike", focusing on policy details over propaganda.
Al Jazeera's Rob Reynolds, reporting from Denver, said Obama had work to do to win over Clinton supporters who felt she was treated poorly during the bitter primary election campaign between the two.
A poll released on Monday showed 30 per cent of Clinton supporters would vote for John McCain, the Republican candidate, a third-party candidate or no one.
McCain attempted to capitalise on allegations of splits within the party by releasing a campaign advertisement featuring a former Clinton supporter now backing him.
Carly Fiorina, a senior aide to McCain said disgruntled female supporters of Hillary Clinton "want a leader whose judgment and experience they can trust".
"We were not all on the same side as Democrats, but we are now ... we are united and we are together and we are determined"
Hillary Clinton, senator for New York
Obama, speaking in Iowa, attempted to play down the rift with Clinton supporters, saying the New York senator had been on his vice-presidential short list.
"I am absolutely convinced that both Hillary Clinton and Bill Clinton understand the stakes," he said.
Fiorina said many Clinton supporters were "stunned" that Joe Biden, the senator who Obama has chosen as his vice-presidential candidate, was praised as a good debater and campaigner.
"Hillary Clinton was clearly, in the Democratic primaries, the woman who ... gathered the most votes - 18 million of them - was a great debater and a great campaigner," she said.
Clinton herself, however, has urged her supporters to back Obama as the Democratic presidential candidate.
"We were not all on the same side as Democrats, but we are now," Clinton told a group of her supporters in Denver on Monday.
"We are united and we are together and we are determined."
Edward Kennedy, the senator for Massachusetts and a longstanding Democratic party icon who now has brain cancer, also made an emotional appearance at the convention, alongside a videotaped tribute to his political career.
Sending a message of political hope for the party, he said: "I have come here tonight to stand with you to change America - to restore its future and to rise to our best ideals, and to elect Barack Obama president of the United States."
Kennedy is the last surviving brother of John F Kennedy, the president who was shot and killed in 1963, and Robert Kennedy, killed while campaigning for the office in 1968.
Kennedy was diagnosed with a brain tumor in May. The US National Cancer Institute has said the outlook for patients with his condition is poor, with average life expectancy depending on the stage of the tumor, from between a few months to up to five years.