The party will seek to burnish Clinton's biography and make its formal nomination on the second day of a convention that began on Monday with anti-Clinton feeling among die-hard Sanders supporters on full and vocal display.
The day's star turn in Philadelphia will be the traditional warm spousal endorsement - with the twist that it will be former President Bill Clinton making the case for his wife to beat Republican Donald Trump in the November 8 election.
"People should really get ready for a show tonight because we're going to have President Clinton talk about the Hillary that he knows," Kristina Schake, a spokeswoman for Hillary Clinton, told CNN.
"He's going to talk about the fights of her life: what she's really stood up for, who she is, the advocate she is and the change maker," she said.
Bill Clinton, president from 1993-2001, draws the admiration of many in the party, but carries some liabilities. Liberals, including Sanders supporters, have long been critical of some of his trademark economic policies, such as the North American Free Trade Agreement (NAFTA) with Mexico and Canada, and Wall Street deregulation.
At his best, Bill Clinton has been known as one of the most powerful political orators in the country: He made an emotional case in 2012 for the re-election of President Barack Obama.
In Tuesday's (local time) prime-time address he will be capping a day Democrats want to use to showcase Hillary Clinton's achievements on issues such as women and families, healthcare and as a former secretary of state. Speakers will include women whose children died from gun violence, some at the hands of police.
Hillary Clinton, 68, will be watching her husband speak from their home in Chappaqua, New York, campaign officials said.
Bill Clinton, 69, has the power to convey the human aspects of a woman who is often seen as hard to read outside her political ambitions and detailed grasp of policy. He feels people should know her as well as he does, and is writing the speech himself, said an aide to the former president.
Clinton supporters see her Washington credentials - she has also been a US senator - as showing she has the experience needed for the White House. Detractors view her as too cozy with the establishment, and with political baggage dating back to the start of her husband's first White House term.
Opinion polls show Clinton as deeply unpopular with some Americans. Recent polls have given her "unfavorable" ratings that average 55.4 percent, according to the RealClearPolitics website. Trump has a similarly poor number, with "unfavorable" ratings averaging 56.9 percent.
She is still disliked enough by some Sanders supporters for ill feelings to have spilled onto the floor of the convention on Monday, with some delegates booing her name.
But she had full support from the stage, with stirring speeches from Sanders and liberal favorite US Senator Elizabeth Warren and first lady Michelle Obama. In her show-stealing address, Obama linked the coming landmark for women to her husband's role as the first black US president.
Controversial Clintons
Sanders, a 74-year-old US senator from Vermont, drew a fervent following of youth and liberals during a primary campaign that called for a tough hand on Wall Street and more aggressive steps to counter social inequality.
Having lit a fire, he struggled on Monday to get his supporters in line. At a meeting before the convention began, Sanders was jeered by his own delegates when he urged them to back Clinton and focus on defeating Trump, a man he called a "bully and a demagogue."
Despite the tensions, the Democratic gathering contrasted with last week's Republican convention in Cleveland that nominated Trump for the White House. Sanders has endorsed Clinton, and the main party leaders all planned to attend.
At the Republican event, the runner-up in the primary, US Senator Ted Cruz, very publicly did not endorse Trump and a slew of party notables stayed away, such as former President George W. Bush and past presidential nominees John McCain and Mitt Romney.
Putting Bill Clinton on as a star turn on Tuesday will certainly not resonate with some Americans, who dislike Hillary Clinton precisely because she is the former president's wife.
In the past, critics attacked her for using her role as first lady to push for healthcare reform. They also criticized her for staying with Bill Clinton through various marital infidelities, including an affair with a White House intern that led to impeachment proceedings against him in 1998 on charges he lied to investigators.
More recently, Republican critics have suggested that the Clinton Foundation, a charity set up by Bill Clinton after he left office, had a corrupting influence on Hillary Clinton while she was secretary of state. The Clintons have denied the allegations, and no wrongdoing has been found.
