Speaking as the first woman nominated for president by a major party, Clinton, the former secretary of state, is giving the highest-profile address of her decades-long political career.
According to excerpts of her prepared remarks released by her campaign, Clinton plans to say that her "primary mission" will be "to create more opportunity and more good jobs with rising wages right here in the United States."
She also will address security threats to the nation and mention recent terrorist attacks.
"The choice we face is just as stark when it comes to our national security," she intends to say. "Anyone reading the news can see the threats and turbulence we face. From Baghdad and Kabul, to Nice and Paris and Brussels, to San Bernardino and Orlando, we're dealing with determined enemies that must be defeated. No wonder people are anxious and looking for reassurance -- looking for steady leadership."
Clinton plans to say that in the country's "moment of reckoning," there are "powerful forces" that "are threatening to pull us apart. Bonds of trust and respect are fraying. And just as with our founders there are no guarantees. It's truly is up to us. We have to decide whether we're going to work together so we can all rise together."
Clinton was introduced by her daughter Chelsea, who called herself "a very, very proud daughter."
Chelsea Clinton highlighted her mother's warmer side, describing her as a caring, loving parent who was always there for her. Her own daughter Charlotte, she said, "loves Elmo, she loves blueberries and above all, she loves facetiming with Grandma."
She also spoke of her mother's public service, saying that she had an up-close view of Clinton's grit and determination in helping help women, first responders and many others.
"She makes me proud every single day," she said. "And mom: Grandma would be so, so proud of you tonight."
One of the dominant themes in the hours leading up to Hillary Clinton's speech was support for the military and law enforcement and a keen awareness of the gravest security threats facing the country.
The earlier speakers included law enforcement officers, retired military officers and parents who lost their children in the line of duty or at war. They often made pressing, emotional pitches for why voters should choose Clinton over Trump to be commander-in-chief.
While the speeches seemed designed to show that persistent GOP claims that Democrats don't care enough about these matters are mistaken, they also exposed a lingering rift in the Democratic Party. As retired Marine Gen. John Allen took the stage, some California delegates rose up in unison with signs and chats of "no more wars!" Others nearby began a counter chant of "U-S-A! U-S-A!" When that didn't work, a couple of delegates shouted for the protesters to "shut up!" and "respect" the general.
Khizr Khan, the father of U.S. Army Capt. Humayun Khan, a Muslim killed in the Iraq War, offered an urgent rebuttal to Trump's call for a temporary ban on Muslims entering the U.S. and for building a wall on the U.S.-Mexico border.
"I ask every patriotic American, all Muslim immigrants and all immigrants to not take this election lightly," he said, during one of the most emotional speeches of the evening. He asked voters to "honor the sacrifice of my son."
He aimed a sharp attack at Trump: "You have sacrificed nothing and no one."
"If it was up to Donald Trump, he never would have been in America," Khan said. "Donald Trump, you are asking Americans to trust you with our future. Let me ask you: Have you even read the U.S. Constitution? I will gladly lend you my copy. In this document, look for the words 'liberty' and 'equal protection of law.'"
Gen. Allen, the former U.S. special envoy in the fight against the Islamic State, made an impassioned case to see Clinton in the Situation Room.
"The stakes are enormous. We must not, we could not stand on the sidelines," he said.
Although he didn't mention the Republican candidate by name, Allen's speech was a direct rebuke to Trump's foreign policy positions. Clinton's America, Allen said, would continue to lead, to uphold its treaties, and to stop the threat of nuclear weapons.
"With her as our commander-in-chief, our international relations will not be reduced to a business transaction. Our armed forces will not become an instrument of torture, and they will not be ordered to engage in murder or carry out other illegal activities," Allen said.
Earlier, transgender rights activist Sarah McBride joined Rep. Sean Patrick Maloney, D-New York, and members of the Congressional LGBT Equality Caucus to address the convention.
McBride, who works as the national press secretary at the Human Rights Campaign Foundation, said she learned the urgency of achieving equal rights and protection for all people after the death of her husband Andrew from cancer four days after their wedding in 2014.
"His passing taught me that every day matters," McBride said. "Hillary Clinton understands the urgency of our fight."
Actress Mary Steenburgen, who appeared with her husband, actor Ted Danson, said Clinton has been a close friend since 1978: "That's a lot of life. How would I describe her? Loves to laugh, especially at herself; world class listener; quick to forgive; sensitive; empathetic. But, like her mother, Dorothy, if she gets knocked down seven times, she will get up eight."
The speakers included several Republicans who said they were choosing Clinton over Trump. Doug Elmets, a former Reagan administration official, in an ode to Lloyd Bentsen's famous rebuke to Dan Quayle about John F. Kennedy in the 1988 vice presidential debate, said in his speech: "I knew Ronald Reagan, I worked for Ronald Reagan. Donald Trump, you are no Ronald Reagan."
Hours before Clinton's speech, the arena was already buzzing and full to the rafters.
In the Wisconsin delegation, the split between supporters of Clinton and defeated primary opponent Sen. Bernie Sanders seemed to be resolved - they were unified in wearing cheeseheads. After a few days of tension, they had agreed to sit in a mixed formation based on who they supported: Clinton-Sanders-Clinton-Sanders.
But elsewhere in the hall, some Sanders diehards opted for a simple but stark display of their dissent from their party: They were wearing neon shirts that stand out brightly in the Wells Fargo Center when the lights dim.
"Enough is enough," the shirts read, quoting the Vermont senator.
In an attempt to prevent Clinton from facing embarrassing jeers from Sanders supporters during her speech, his team texted supporters Thursday evening to encourage them to "extend the same respect during Secretary Clinton's speech" that her supporters did during his remarks.
Republican nominee Donald Trump released a statement hours ahead of Clinton's speech in an effort to undercut his rival by arguing that she and her top surrogates have glossed over the country's most pressing problems.
"At Hillary Clinton's convention this week, Democrats have been speaking about a world that doesn't exist," said Trump. "A world where America has full employment, where there's no such thing as radical Islamic terrorism, where the border is totally secured, and where thousands of innocent Americans have not suffered from rising crime in cities like Baltimore and Chicago."
