Mr Inslee, 68, will make climate change his number one issue, calling it "the most urgent challenge of our time" in his first campaign video.

He is the first governor to throw his hat into the ring, joining 12 other Democrats, including six senators.

The two-term governor has been a fierce critic of President Donald Trump.

"I'm running for president because I am the only candidate who will make defeating climate change our nation's number one priority," Mr Inslee says in the video, released on Friday.

Mr Inslee's mid-term elections campaign ran on the platform of creating new energy jobs - his 2020 campaign video echoed the same, tying "defeating climate change" with transforming the economy.

Elizabeth Warren, Kirsten Gillibrand, Amy Klobuchar, Kamala Harris and Bernie Sanders are among other declared contenders for the Democratic primary in 2020, the first time more than one woman has competed.

Unmatched progressive credentials

By Anthony Zurcher, BBC News, Washington

Jay Inslee is someone who in the past would be a naturally formidable presidential candidate. He's a veteran politician with the kind of executive experience that comes from being a governor of a mid-sized state.

This isn't your father's Democratic Party, of course, and with a diverse range of candidates already in the race, Mr Inslee will be pressed to find breathing room for his campaign.

His answer is to fashion himself as the environmental candidate. With the Green New Deal getting traction among progressives, Mr Inslee is touting his work addressing climate change in Washington state. He's launching his presidential bid at a solar panel factory whose success he attributes to his policies as governor.

If Mr Inslee gets the attention of Democratic voters with his environmental pitch, he can then pivot to talking about his efforts to fight the Trump administration's immigration policies, expand healthcare in his state, raise the minimum wage, enact paid family medical leave, end capital punishment and pardon Washington residents previously convicted of now-legalised marijuana drug offences.

It's a record of progressive accomplishment that the half-dozen senators already in the race, having toiled in the minority since 2014, can't match.