Ryan is serving a six-and-a-half year sentence on corruption charges. He has served four-and-a-half years of that sentence.
The decision represents a victory for the former governor, with the potential of shaving off some of his prison time.
"I think it's fair to say that he was very happy," said Jim Thompson, Ryan friend and attorney. "He was very grateful to the Supreme Court for giving him this chance. "
Ryan's attorneys have argued that the jury instructions in his trial were flawed.
The 7th Circuit Court of Appeals in Chicago ruled earlier that Ryan didn't make a timely argument on that subject so the convictions and sentence should stand. But now the Supreme Court says the argument about jury instructions can be made, and the circuit court needs to re-think the issue.
"If the 7th Circuit comes to the conclusion that the jury instructions were erroneous, then they're going to have to send it back for a new trial," said Prof. Richard Kling, Kent College of Law.
That's one possibility, but many consider it unlikely that Ryan would be retried on a limited number of charges. Furthermore, by the time it might come to trial, Ryan will already have served most, if not all, his sentence.
"This isn't going to shorten his sentence very much," said Prof. Leonard Cavise, DePaul College of Law. "Even if they send it back to district court on a couple of those counts, you can't get much done in the next six months or so."
Ryan is serving his time at the federal prison camp in Terre Haute. His scheduled releae date from federal custody is Independence Day, 2013. But one thing that could happen more immediately is that his attorney's would ask for an appeal bond, presenting the possibility that Ryan could be released on bond while the appeals court decides what to do next.
Thompson said the decision has not yet been made on whether or not to seek an appeal bond.
"Some people have done that," he said. "Conrad Black did that. He got the Supreme Court sending his case back to the 7th Circuit and won some and lost some and had to go back."
That's the down side, according to Thompson. You might win an appeal bond and get to come home, but then you could lose the appeal and have to return to prison -- when you've technically got 14-months and some days left in your sentence.
The appeal bond decision likely won't come until late June when both the Ryan defense team and the government outline their arguments in where the appeal should go.