"Americans are deeply disappointed and hurt by the way they're treated by what they think is the power elite in Washington, D.C.," Steyer said in his campaign announcement.
Earlier this year, Steyer decided that he wasn't going to run. Instead, he put his efforts towards impeaching President Trump.
"The fact that he is coming back at it after having already bowed out and we have such a crowded field is a little surprising to a lot of folks I think," Jeremy White, a California Politico reporter, said.
MORE: Who's running for president in 2020? List of Democratic candidates
Steyer did not mention impeachment efforts during his campaign announcement. He's casting himself as an outsider and opposing what he called the "corporate takeover of our democracy."
"I think people believe that the corporations have bought the democracy," Steyer said. "That the politicians don't care about or respect them."
White doesn't think it's exactly clear how Steyer will break out from the pack of other presidential hopefuls.
"Tom Steyer has a couple things going for him," White said. "He has plenty of money to spend. As he's demonstrated, willing to put his own money into politics, and his push to impeach Donald Trump. He has gotten a lot of folks to sign on to that. So, he has sort of a ready-made donor data base."
Steyer said he's grown frustrated at the pace the Democratic-controlled House is approaching the president. We expect to hear more about that throughout his campaign.
There are 20 spots at the debate, but two dozen people have their hat in the ring. If more than 20 people qualify, the Democratic National Committee will hold a tiebreaker to determine who gets on stage.
See more stories on the 2020 presidential election.