Michelle Obama addresses the crowd at the Democratic National Convention at the Pepsi Center in Denver on Monday. (Darin McGregor/Rocky Mountain News/Associated Press)

Michelle Obama described herself and husband Barack as people guided by American values and a desire to improve the world for their two daughters and all American children in a speech to the Democratic National Convention on Monday night.

Obama was the showcase speaker on the opening day of the four-day convention in Denver, where her husband will be confirmed as the Democratic presidential candidate.

Her speech was punctuated by frequent applause and cheers, and drew a long standing ovation at the end.

Obama said she and her husband were raised with the values shared by many Americans: "that you work hard for what you want in life; that your word is your bond and you do what you say you're going to do; that you treat people with dignity and respect, even if you don't know them, and even if you don't agree with them.

"Barack and I set out to build lives guided by these values, and pass them on to the next generation," she said.

"We want our children — and all children in this nation — to know that the only limit to the height of your achievements is the reach of your dreams and your willingness to work for them," Obama said.

She also stressed her role as a mother.

"I come here as a mom whose girls are the heart of my heart and the centre of my world. They're the first thing I think about when I wake up in the morning, and the last thing I think about when I go to bed at night," she said.

Obama's mission was to try to show delegates her husband's human side, as she has done in speeches and interviews since his campaign was launched more than 18 months ago.

Before she spoke, delegates were shown a biographical film called "South Side Girl," which was narrated by her mother. She was introduced by her brother, Craig Robinson, the head basketball coach at Oregon State University.

Barack Obama watched his wife's speech from the living room of a family in Kansas City, Mo., and appeared by video moments afterward.

"How about Michelle Obama?" he asked the crowd. "Now you know why I asked her out so many times even though she said no. You want a persistent president."

The girls responded to their father on the giant screen with "Hi, Daddy!" and "I love you, Daddy."