Trump's remarks - where he hit on recent political themes of rejecting communism, Save America Act legislation he favors and the right to bear arms - wrapped up just before midnight at the Freedom 250 event.
"Long live the cause of independence," he said. "May it reign forever and ever and ever, we will always be on top, we will never let our country fall, we will always be the best."
Upon closing, he told the crowd, "this is only the dawn of the golden age of America" with its destiny "written by God".
The grande finale of the fireworks show was marked by a massive flurry of blasts - reaching a much anticipated crescendo. As it concluded around 1am, the small crowd on Capitol Hill cheered and rapidly started heading for the exits in a light rain.
The celebration, which included a flyover - one featuring the new Air Force One jet - a concert - as well as the speech and fireworks was delayed by a thunderstorm that forced an evacuation of the National Mall in the early evening.
Freedom 250 asked guests in the area attending Salute to America, the Great American State Fair and Fifa fan zone events to seek temporary shelter in a nearby buildings. Throughout the day, the capital had broiled under 100F (37C) temperatures - part of a larger heat wave enveloping the eastern US.
Also in Washington, about 400 members of the white nationalist group Patriot Front were seen carrying US flags while marching in unison through the streets of the capital.
Videos posted to social media and the group's own Telegram channel showed the masked, uniformed members marching near the Capitol building and Union Station, the city's main passenger rail hub.
The group was founded in 2017 following violence at the Unite the Right rally in Virginia, breaking off from another group.
Americans tried to keep cool during celebrations during a sweltering heat wave on the US East Coast that cancelled festivities earlier this week.
On Friday, organisers of the National Park Service's Independence Day Parade in Washington DC cancelled the annual event over safety concerns. Some celebrations also were shut down in New Jersey, Pennsylvania and Maryland - and as far west as Colorado.
The highest temperatures were expected in Maryland, Delaware and New Jersey, where the mercury could reach 108F (42C).
On the National Mall in Washington volunteers handed out bottles of water from buckets of ice before sunshine gave way to thunderstorms.
Nearly 750,000 went without power in the east due to extreme weather with another 150,000 in New Jersey, according to tracker Power Outage.
Energy company DTE said that severe weather, including winds over 60mph (97km/h) on Friday evening in Michigan, left more than 350,000 homes in the state without power.
Other states affected include Pennsylvania, Illinois, Ohio, New York and Wisconsin.
All four living former US presidents also shared messages to celebrate the milestone. President Joe Biden, Trump's predecessor, recalled the Independence Declaration's edict that all people are created equal.
"We chose that path 250 years ago but that's where the work began, not where it ended," he said before warning that the nation's promise of equality for all was still a work in progress.
The country's first black president, Barack Obama, reshared excerpts of a recent speech he made at his presidential museum's opening.
"There's more to do to fulfil the nation's founding ideals," he said. "Every generation must take up the unfinished work of the last and carry it further - protecting what's right, fixing what's wrong, and making our union a little more perfect."
The 43rd president George W Bush said "the next 250 years require Americans to be citizens, not spectators".
Americans need to "take an active interest in the health and welfare of our country and the communities in which they live", he said.
His predecessor Bill Clinton took a moment to comment on US politics today.
"Today, we celebrate this milestone amid another period of deep division, renewed questions about America's future and role in the world, and serious threats to our own institutions and to our democracy itself," the 42nd president said.
Kwasi Asiedu contributed to this report.
