The Florida Supreme Court ruled 6-1 Friday that he can run as the Reform Party presidential candidate in the November election.
The decision met a Saturday deadline for mailing 25,000 ballots to overseas voters, most of them military personnel, and ended a dizzying two weeks during which Nader was on and off the ballot.
"This is a case that should have been thrown out of the courts sooner," said Nader campaign spokesman Kevin Zeese.
As the Green Party candidate in 2000, Nader attracted 97,000 Florida votes - and most Democrats and many Republicans agree that those votes cost Democrat Al Gore the presidency.
President Bush won the state by 537 votes after five weeks of recounts and legal fighting - much of it before Florida's high court.
This year, the Reform Party of Florida submitted Nader to the state as its candidate but the Florida Democratic Party and several individual voters challenged his certification as the Reform Party candidate.
The key legal challenge against Nader was the contention that the Reform Party was no longer a bona fide national party and didn't nominate Nader in a national convention - as required by Florida law - but instead on a conference call three months earlier.
Officials with the Party and Nader argued that the Reform Party convention may have been a small but that it had legitimately confirmed him as their presidential nominee.
The Reform Party, which formed in 1995 out of Ross Perot's 1992 and 1996 presidential bids, has seen its membership decline amid infighting in recent years. Its national treasurer last month said the party had $18.18 in the bank.
A state judge last week ordered Secretary of State Glenda Hood, Florida's top elections official, to strike Nader from the ballot. Hood, who was appointed by Gov. Jeb Bush, complied.
But when Hood appealed that order, an automatic suspension was triggered. So Nader was back on the ballot.
On Wednesday, Circuit Judge Kevin Davey again ordered Hood to take Nader off as the case was appealed to the state's high court.
Now, he is back on again after the Supreme Court's decision.
Scott Maddox, chairman of the Florida Democratic Party, said he didn't think an appeal was likely even though he thought the party made its case at the trial level.
The Reform Party of Florida greeted the decision with relief, said spokesman Patrick Slevin. But the party is also angry that it had to defend itself and its candidate, he added.
Alia Faraj, a spokeswoman for Secretary of State Glenda Hood, said elections supervisors would be able to meet Saturday's deadline.
"All along the secretary's goal ... was finality," she said.
In Friday's majority opinion, Florida's high court wrote that it couldn't tell whether state lawmakers wanted the terms "national party" and "national convention" interpreted strictly or broadly.
"In the absence of more specific statutory criteria or guidance from the Legislature, we are unable to conclude that a statutory violation occurred," the court wrote.
Chief Justice Barbara Pariente and Justices Charles Wells, Peggy Quince, Raoul Cantero and Kenneth Bell concurred in the majority opinion. Justice R. Fred Lewis concurred in the result but not the opinion. Justice Harry Lee Anstead dissented, saying he would have upheld Davey's ruling.
"In essence, the trial court held that no matter how narrowly or broadly the terms of the statutes are defined, those terms were not met here," he said.
Nader is now planning a nine-city tour of Florida at the end of the month, starting in Jacksonville and working his way south to Miami.
Nader hopes to touch on such issues as the U.S. withdrawal from Iraq, living wages for Americans and the nation's health care.
"We hope to engage the Democrats on the issues and hope they will stop their undemocratic activities," Zeese said.
Democratic National Committee Chairman Terry McAuliffe said in a statement that, "The fact that Ralph Nader secured a place on the Florida ballot by means of the Pat Buchanan Reform Party speaks for itself. In state after state, Nader has become an extension of the Republican Party and their corporate backers."
Maddox, the head of Florida's Democrats, had his own zingers.
"I think we showed pretty clearly on the trial court level that the Reform Party was a sham," he said. "Jeb Bush and Glenda Hood did everything they could to keep Ralph Nader on the ballot."