State Supreme Court justices agreed to expedite the case, but they gave no specific time frame. They planned to review legal briefs only and would not hold oral arguments.
Emanuel has asked the court to overturn a lower ruling that pulled his name off the ballot because he had not lived in the city for a year. His attorneys called Monday's decision "squarely inconsistent" with previous rulings on the issue.
The moves by the high court bought valuable time for Emanuel. The Chicago Board of Elections had said it would begin printing ballots without his name as early as Tuesday, with the election less than a month away. Absentee ballots were to be sent out within days.
Messages left for election officials were not immediately returned.
"I'm confident in the argument we're making about the fact that I never lost my residency," Emanuel said Tuesday at a campaign stop where he picked up an endorsement from the Teamsters Joint Council.
Emanuel said the order on the ballot printing was "an important first step in ensuring that voters are not disenfranchised and that they ultimately get to choose the next Mayor of Chicago."
In their appeal, Emanuel's attorneys called Monday's ruling "one of the most far-reaching election law rulings" ever issued in Illinois, not only because of its effect on the mayoral race but for "the unprecedented restriction" it puts on future candidates.
His lawyers raise several points, including that the appeals court applied a stricter definition of "residency" than the one used for voters. They say Illinois courts have never required candidates to be physically present in the state to seek office there.
By adopting this new requirement, the court rejected state law allowing people to keep their residence in Illinois even if they are away doing work for the state or federal government, the appeal said.
Emanuel, a former congressman who represented Chicago, was gone while he served as President Barack Obama's chief of staff for nearly two years.
The new standard also sets a "significant limitation on ballot access" that denies voters the right to choose certain candidates, the appeal said.
Just hours after Monday's ruling, the campaign to replace retiring Mayor Richard M. Daley began to look like an actual race.
For months, three of the main candidates struggled for attention while Emanuel outpolled and outraised them, blanketed the airwaves with television ads and gained the endorsement of former President Bill Clinton, who came to town to campaign for Emanuel.
Former Sen. Carol Moseley Braun, city Clerk Miguel del Valle and former Chicago schools chief Gery Chico suddenly found themselves in the spotlight - and trying to win over Emanuel supporters who suddenly may be up for grabs.
Even as Emanuel vowed to fight the decision, Braun urged voters to join her campaign "with your time, your effort or your money."
Reporters surrounding Chico outside a restaurant asked him if he was a front-runner - something that seemed inconceivable last week when a Chicago Tribune/WGN poll showed him with the support of just 16 percent of voters surveyed compared with a whopping 44 percent for Emanuel. The same poll showed Braun with 21 percent support, and del Valle with 7 percent.
"I'm trying to get every vote I can from everybody in this city," said Chico, who released records last week showing he had just over $2 million at his disposal, about one-fourth of the money available to Emanuel.
In their 2-1 ruling Monday, an appeals court said Emanuel met the requirements to vote in Chicago but not to run for mayor because he had been living in Washington.
Challengers to Emanuel's candidacy argued the Democrat did not qualify because he rented out his Chicago home and moved his family to Washington to work for President Barack Obama for nearly two years. Emanuel - who quit his job and moved back to Chicago in October after Daley announced he would not to seek a seventh term - has said he always intended to return to Chicago and was living in Washington at the president's request.
If he doesn't win the appeal, the race takes on a whole new dynamic. In a city with huge blocs of black, white and Hispanic voters, the Chicago Tribune/WGN poll showed Emanuel leading among all of them, even though his three top rivals are minorities.
Laura Washington, a local political commentator who writes a column for the Chicago Sun-Times, said if Emanuel is out, Chico, who is Hispanic, could be the big winner in terms of fundraising.
"Rahm has the establishment support, the civic leaders, business community, the money class. And Chico is as close to that type of candidate as anyone," Washington said. "They'd take Chico as a second choice, easily."
Braun would be the big winner among black voters, she said. The recent poll showed Emanuel with the support of 40 percent of black voters compared with 39 percent for Braun, even though two other prominent black candidates dropped out of the race to try to unify the black vote.
Del Valle, another Hispanic candidate, said Emanuel's quandary bodes well for the other candidates, regardless of what the court does.
"Now voters see there's an opportunity to look at the field and give candidates either a second look or in some cases a first look," del Valle said. "People are going to pay more attention to the other candidates."
Associated Press writers Don Babwin, Deanna Bellandi, Sophia Tareen and Michael Tarm contributed to this report.