On the final night of the four-day Democratic National Convention, Harris, 59, promised to be a "realistic" and "practical" president for all Americans, as she battles Trump, 78, in a razor-close campaign.
"In the enduring struggle between democracy and tyranny, I know where I stand and I know where the United States belongs," she said on Thursday, accusing Trump of bowing down to dictators.
Kamala Harris said she would defend US interests and warned that dictators "are rooting for Trump". (EPA PHOTO)
She promised to back NATO, Ukraine and "stand up to Putin's aggression", a reference to Russia's president.
Harris emerged as the Democratic candidate little more than a month ago when allies of President Joe Biden, 81, forced him to quit the race.
It was a forceful speech for a candidate who, during her brief campaign, had yet to articulate much of her vision for the country.
Harris has faced a stream of personal attacks from Trump, who called her weak on the foreign stage.
After days of protests from Palestinian supporters who were disappointed at not getting a speaking spot at the convention, Harris delivered a pledge to secure Israel, bring the hostages home from Gaza and end the war in the Palestinian enclave.
Chicago's United Center brimmed with energy - and people - on the convention's final day. (EPA PHOTO)
"Now is the time to get a hostage deal and a ceasefire deal done," she said to cheers on Thursday night.
"And let me be clear, I will always stand up for Israel's right to defend itself and I will always ensure Israel has the ability to defend itself."
She said she wanted to end the war in a way that provides for Israel security and allows the Palestinian people to realise their right to self-determination.
Harris said she would take whatever action was necessary to defend US interests against Iran and said tyrants and dictators, including North Korea's Kim Jong-un, "are rooting for Trump".
If successful, Harris stands to make history as the first woman elected US president on November 5.
Kamala Harris was joined by husband Doug Emhoff along with running mate Tim Walz and his wife Gwen. (AP PHOTO)
Harris drew a series of contrasts with Trump, accusing him of not fighting for the middle class, planning to enact a tax hike through his tariff proposals, and having set in motion the end of a constitutional right to abortion with his picks for the US Supreme Court.
Harris noted the Supreme Court's recent ruling about presidential immunity and the risks that would pose if Trump gained power again.
"Just imagine Donald Trump with no guardrails," she said.
Trump, who had promised to respond to Harris' speech in real time, posted a series of messages on Truth Social as she spoke about him, including: "She stands for Incompetence and Weakness - Our Country is being laughed at all over the World!" and "She will never be respected by the Tyrants of the World!"
Harris also said she would pass a middle tax cut that would benefit more than 100 million Americans, contrasting that with Trump's vow to cut the corporate tax rate.
Vice-President Kamala Harris and second gentleman Doug Emhoff embraced after her speech. (AP PHOTO)
She discussed her plans to fight for abortion rights, voting rights legislation, boost the housing supply and ban what she has called "price gouging" by grocers.
Her campaign has also proposed raising the corporate tax rate from 21 per cent to 28 per cent.
Chicago's United Center brimmed with energy - and people.
The arena's 23,500 seats were filled and arena staff briefly blocked more people from entering the facility, saying the city's fire marshal declared the building at capacity.
"We did it," Harris told supporters at a post-convention reception. "Forward, forward, forward."
