The Illinois Supreme Court ruled unanimously on Thursday that Rahm Emanuel can run as a candidate for mayor in next month’s Chicago elections, overturning an appeals court decision that had knocked the former White House chief of staff off the ballot.

The scathing majority opinion from five of the justices on the Illinois Supreme Court scolded the appellate court for adopting a previously unheard of test for residency in Illinois, saying it was without any foundation in Illinois law.

In reversing the 2-to-1 appellate ruling, the justices said what it means to be a resident for election purposes was clearly established long ago and Illinois law has been consistent on the matter for well over a century.

Two justices concurred with the majority in ruling Emanuel eligible for the ballot, but wrote a separate opinion stating the law is not as clear-cut as the majority states.

Emanuel lived for nearly two years in Washington working for President Obama until he moved back to Chicago in October to run for mayor.

Emanuel, who has said he always intended to return to Chicago and was only living in Washington at the request of the president, had asked the Supreme Court to overturn the Feb. 22 appeals court ruling.

Within minutes of the ruling, Emanuel was at a downtown Chicago public transit station shaking hands with residents.

He never stopped campaigning as the controversy evolved. His spokesman said Emanuel was en route to the campaign appearance when he received word of the ruling and was scheduled to participate in a televised debate Thursday evening.

The mayoral race and Emanuel’s campaign had been thrown into disarray after the appellate court ruling on Monday. The following day, the state Supreme Court ordered Chicago elections officials to stop printing ballots without Emanuel’s name on them. Chicago election officials said they had printed nearly 300,000 ballots without Emanuel’s name before they abruptly stopped.

Emanuel had been the heavy favorite to lead the nation’s third-largest city, and had raised more money than any of the other candidates vying to replace Mayor Richard M. Daley, who announced he was retiring after more than two decades as mayor.

Meanwhile, the other main candidates in the race — former Sen. Carol Moseley Braun, City Clerk Miguel del Valle and former Chicago schools chief Gery Chico — moved quickly to try to win over Emanuel supporters.

The residency questions have dogged Emanuel ever since he announced his candidacy last fall. Emanuel tried to move back into his house when he returned to Chicago but the family renting it wanted $100,000 to break the lease and move out early. The tenant, businessman Rob Halpin, later filed paperwork to run for mayor against Emanuel, only to withdraw from the race a short time later.

The Supreme Court was also impressed with Emanuel’s testimony before the city’s election board in which he listed all the personal items in the house he rented out in Chicago when he moved to Washington, including his wife’s wedding dress, photographs of his children and clothes they wore from the hospital as well as items belonging to his grandfather.

“The Board determined that, in this situation, the rental did not show abandonment of the residence,” the court wrote. “This conclusion was well supported by the evidence and was not clearly erroneous.”

The Chicago Board of Election Commissioners and a Cook County judge has previously both ruled in favor of Emanuel, a former congressman, saying he didn’t abandon his Chicago residency when he went to work at the White House.

NPR’s David Schaper contributed to this report, which includes material from The Associated Press Copyright 2011 National Public Radio. To see more, visit http://www.npr.org/.