Republican attorney Linda A. Kerns submitted papers with the U.S. District Court Monday saying she had "reached a mutual agreement that Plaintiffs will be best served" if she withdrew.
She was joined in the motion by two other attorneys -- colleagues who only recently signed on to the case with her.
Kerns is a veteran of election law battles in Pennsylvania and has written publicly about her desire to see voter ID laws passed to prevent election fraud.
She had served as the primary attorney on the central Trump campaign lawsuit in Pennsylvania challenging the election's outcome. It is not clear why she has asked to step aside.
Over the weekend, the Trump campaign asked the court to sanction lawyers at a firm helping defend the state in the case, saying someone from the firm left a harassing message on Kerns' voicemail.
Lawyers from Ohio firm of Porter Wright Morris & Arthur recently asked to withdraw from the federal lawsuit the Trump campaign filed in Pennsylvania to challenge the election results there.
On Friday President Donald Trump installed Rudy Giuliani to lead the legal efforts he has mounted to resuscitate his failed bid for a second term in office, a move that came after a series of court defeats on Friday, two sources told ABC News.
A spokesperson for Giuliani confirmed his expanded role for the president.
Biden holds a lead of more than 59,500 votes in Pennsylvania. On Friday, the Trump campaign suffered adverse rulings in six cases in the state, which together determined that 8,921 votes the Trump legal team had contested would not be tossed out.
Since Election Day, Giuliani has been a public face of the president's legal campaign. He has headlined a series of press conferences to claim, without support, that the mishandling of the election and fraud cost Trump the race, despite purported evidence that has been exposed as weak in court.
The announcements from the Trump lawyers seeking to step away came after progressive groups announced protests in front of law firm offices in Washington to protest the president's legal challenge to the election.
"These law firms have been under tremendous pressure as it became clear these claims were baseless, and that they were part of a broader campaign to delegitimize the election," Wendy Weiser, from the Brennan Center for Justice, a bipartisan law and public policy institute, told ABC News. "This was not an appropriate use of the court system."