Washington is "corporate occupied territory" that turns the government against the interest of its own people, Nader said.
"In that context I have decided to run for president."
He had been accused by many Democrats of handing the 2000 election to George Bush, the then Republican contender.
Standing as a Green party candidate that year, Nader took some 97,000 votes in Florida.
His candidacy provoked claims that he had siphoned off support from Al Gore, the former vice-president, in that key state.
Four years later, Nader won just 0.3 per cent of the national vote as an independent when he appeared on the presidential ballot in only 34 states.
'Different perspectives'
Nader said in Sunday's interview that he would offer different perspectives on issues such as the environment, workplace safety and corporate interests.
He called John McCain, the leading Republican candidate for the nomination, "the candidate for perpetual war".
He also criticised Barack Obama, the current Democratic frontrunner, saying that his "better instincts and his knowledge have been censored by himself".
Obama, an Illinois senator, is attempting to defeat rival Hillary Clinton in contests in Ohio and Texas on March 4.
Anybody had the right to run for president if they qualified, he said on Saturday.
Obama camp reaction
Obama said: "I think the job of the Democratic Party is to be so compelling that a few percentage of the vote going to another candidate is not going to make any difference."
But a website campaigner for him was hostile to Nader's decision to run in November.
"We're saddened but not surprised by Ralph Nader's announcement," John Pearce, director of the website campaign RalphDontRun.com, said.
"We continue to strongly believe that any third party candidacy in the US two-party system has the inevitable effect of helping elect those most hostile to one's agenda.
"In this case, that means helping elect Republicans."