He told supporters in Pennsylvania that he was keeping "one promise after another", dismissing criticism as "fake news" by "out of touch" journalists.
Trump decided to skip the White House Correspondents' Dinner - the first U.S. leader to miss the event since an injured Ronald Reagan in 1981.
Turning to his election pledges, Trump said the first 100 days had been "very exciting and very productive".
He said he was "delivering every single day" by:
- Ending "jobs theft" and bringing them back to the U.S. from overseas
- Easing regulations on energy exploration, including halting a "war on coal"
- Pulling out of international deals not beneficial to the U.S., including the Trans-Pacific Partnership
On climate change, Trump said "a big decision" would be taken within the next two weeks.