Steyer started the "Need to Impeach" initiative on Friday with an advertisement calling on Americans to pressure their members of Congress to vote the president out of office.
The billionaire environmentalist who endorsed Trump’s Democratic rival, Hillary Clinton, in the 2016 race, has sent letters to congressmen and governors around the country urging them to take action against the "dangerous" president.
"He's brought us to the brink of nuclear war, obstructed justice at the FBI, and in direct violation of the Constitution, he's taken money from foreign governments and threatened to shut down news organizations that report the truth," Steyer said in the campaign video.
"If that isn't the case for impeaching and removing a dangerous president, then what has our government become?" he added.
Steyer said that “this president represents a clear and present danger, who's mentally unstable and armed with nuclear weapons.”
The former hedge-fund manager is funding the impeachment campaign, according to its website.
In his letter, Steyer called on all 50 governors and 2,000 city mayors countrywide to publically oppose Trump. The letter was obtained by The Hill.
A majority vote in the US House of Representatives is necessary to impeach a president, which would lead to a trial in the Senate, where a two-thirds majority is essential for conviction.
A majority of American voters believe Trump is not "fit to serve as president" of the United States, according to a recent poll.
Another recent poll has found most Americans disapprove of Trump’s leadership and see him as a divisive figure who has not fulfilled his campaign promise to positively change the US government.
Trump has been widely criticized for his response to the deadly white supremacist rally in Charlottesville, Virginia, after he said "both sides" were to blame for the violence.
Critics say that Trump’s divisive rhetoric and policies against immigrants and minorities before and after his election have emboldened far-right groups and promoted hate crimes across the country.