Hillary Clinton urged supporters "not to give up" in her first public appearance since she suffered a shocking defeat to Republican Donald Trump in the November 8 presidential election.
"I know many of you are deeply disappointed about the results of the election," she said to the crowd on Wednesday night at the Children's Defence Fund gala in Washington.
"I am too, more than I can ever express."
The former secretary of state said appearing in public was not the easiest thing for her, NBC News reported.
"There have been a few times this past week when all I wanted to do is just to curl up with a good book or our dogs and never leave the house again," Clinton said.
Nevertheless, the former presidential nominee attempted to inspire her audience and emphasised a line of Martin Luther King Jr. that is often quoted by President Barack Obama: "The arc of the moral universe is long, but it bends toward justice."
"The divisions laid bare by this election run deep, but please listen to me when I say this... America is worth it. Our children are worth it. Believe in our country, fight for our values and never, ever give up," she added.
During the rest of her speech, she emphasised bipartisanship, advocacy, volunteerism and investing in the children of the US - no matter their race, religion or immigration status, NBC News said.
At the event, Clinton was introduced by Marian Wright Edelman, a longtime friend and mentor who founded the Children's Defence Fund in 1973.
"I am so proud of her in so many ways," Wright Edelman said, before noting that Clinton is leading in the popular vote. "So we're going to say she's the people's president".
After the brief trip to Washington, Clinton was set to return to New York. She has no further public events on her immediate calendar.