"We're in this race to win," the 73-year-old Sanders, an independent lawmaker who is little known outside political circles and his home state of Vermont, told reporters at a low-key, rushed announcement on the lawn outside the US Capitol, where he has served in Congress since 1991.
By jumping into the presidential race, the self-described socialist Sanders presents a long-shot challenge to Democratic frontrunner Hillary Clinton but said he relishes the chance to go toe-to-toe with her in "serious debates over serious issues -- not political gossip."
"Ninety-nine percent of all new income generated in this country is going to the top one percent," he said.
"That type of economics is not only immoral, it's not only wrong, it is unsustainable."
Sanders is vehemently opposed to recently implemented laws that relaxed campaign finance rules, which he said allows billionaire donors to buy candidates of their choosing.
And he reiterated his fierce opposition to a massive trade pact under negotiation with Asia-Pacific nations, saying the deal would cost American jobs.
He eventually won a seat in Congress in 1990. He voted against authorizing the use of military force against Iraq in 1991 and again in 2002, when Clinton voted in support of the Iraq war resolution.
