Eakin's resignation was a dramatic development in the saga that has unfolded since Attorney General Kathleen G. Kane revealed in 2014 that her office had been a hub for the exchange of email messages containing pornography and jokes that mocked African Americans, women, gays, lesbians, and others.
Since then, more than a half-dozen public officials have lost their jobs, including high-ranking members of former Gov. Tom Corbett's administration.
Seamus McCaffery, a Philadelphia Democrat, resigned his Supreme Court seat soon after the scandal erupted.
Eakin was charged last year with violating judicial ethics rules for his involvement with offensive email messages. In bringing the charges, the state's Judicial Conduct Board said Eakin had tarnished the Supreme Court and his position on the bench by exchanging the emails.
The majority of Eakin's emails were exchanged with friends, and were sent or received on his private account. They were captured on state government servers because one of his friends was a prosecutor at the Attorney General's Office and used his work email account.
Eakin, 67, a Republican from Cumberland County, faced a trial on the charges before the Court of Judicial Discipline this month.
Costopoulos said Eakin's resignation would not necessarily halt that process or spare the justice's pension.
"There is no deal," Costopoulos said, adding that it was up to the Court of Judicial Discipline whether to continue the ethics case against Eakin.
A spokeswoman for the judicial court said Tuesday it would have no comment on Eakin's resignation.
Eakin's decision to step down appeared to be a bid to save his taxpayer-paid pension from his 20 years of service on the appellate courts, an annual sum estimated at about $153,000.
That retirement benefit is on top of and apart from his pension from 20 years as a prosecutor in Cumberland County, 11 of those as district attorney.
It remained unclear whether Eakin's decision to step down would win him favor with the judicial court or set the stage for a more lenient outcome should there be a trial.
In previous cases, the court has forged ahead with disciplinary proceedings even after judges resigned.
Most recently, in January, the court ruled that former Philadelphia Traffic Court President Judge Michael Sullivan had brought his judicial office into disrepute by fixing tickets. Sullivan had resigned from the bench eight months earlier.
Sullivan is scheduled for a hearing next month, at which the court is to decide whether to revoke his yearly pension, estimated at about $35,000.
The decision in the Sullivan case was written by Judge Jack Panella, who has been presiding over the Court of Judicial Discipline's three-judge panel assigned to Eakin's case.
Eakin has apologized for the emails. He has said that they do not reflect his character and that his judicial opinions over the last two decades were based on thoughtful reasoning and facts, not biases.
"His work product and his opinions are completely devoid of prejudice," Costopoulos said Tuesday.
Through his lawyers, Eakin has emphasized that he received, rather than sent, the majority of the offensive emails. To them, that was an important distinction, as it has been revealed over the last few months that other judges - including several Supreme Court justices - had received emails similar to those sent to Eakin.
"This is a very slippery slope we are on. I think it's a very dangerous time we are in," Costopoulos said.
"This is the only process I know of in America where you can be charged with sending emails to friends that were inappropriate and face the death penalty," he said. "I just don't think that's right."
Kane revealed the existence of the pornographic emails two years ago. Though she has publicly released some of the messages, critics accuse her of releasing only those of her political enemies, as she has refused to make public the entire trove of messages in her possession.
She never made Eakin's emails public. She was forced to turn those and other messages involving justices over to the Supreme Court in late 2014. After two reviews, Eakin was cleared of wrongdoing.
A year later, Kane accused judicial ethics officials of whitewashing Eakin's behavior. The scandal swiftly grew into a controversy over the tepid response to Eakin's offensive messages.
Both the high court and the Judicial Conduct Board - the investigative and prosecutorial agency that brings charges to the judicial court - had initially dismissed Eakin's emails as unworthy of rebuke. The court's expert called them "unremarkable," while the conduct board's chief counsel said they were at worst "mildly pornographic."
But news accounts later revealed that the board's counsel at the time was an old friend of Eakin's who had recently worked on his campaign, and that one of the board's members had also received pornography traded on state computers.
After those revelations, the Judicial Conduct Board and the Supreme Court began investigating anew, and both reached harsher conclusions. The Supreme Court's new expert called Eakin's emails "offensive, tasteless, insensitive, juvenile, and repugnant to reasonable sensibilities."
As he awaited trial on ethics charges, Eakin was suspended with pay by the Court of Judicial Discipline, which said his continued presence on the bench harmed the public's trust in the judiciary.
Costopoulos said Tuesday that he hoped Eakin could keep his pension.
After it became public that McCaffery had exchanged hundreds of pornographic emails, he resigned from the bench under a deal in which he was able to keep his pension and avoid any inquiry into whether he had violated judicial ethics rules.
Eakin, too, had negotiated a deal with the Judicial Conduct Board in an effort to settle the ethics matter without a public trial. But at a tense court hearing last month, the judicial court refused to hear the terms of the proposed deal - although it had brought in prominent Philadelphia lawyer Richard A. Sprague to help mediate the case.
Eakin's resignation leaves a vacancy on the seven-member court, which now has five Democratic justices and one Republican.
Gov. Wolf said he intends to nominate someone to fill the vacancy until the next judicial election in 2017. The Senate would have to confirm any nominee.
Of Eakin's resignation, Wolf said: "I believe he did the right thing. ... He did something that I think helps build the kind of trust we need to build in our institutions."