Joe DeFelice, chairman of Philadelphia's Republican City Committee, resigned Friday and is expected to soon take a job with President Trump's administration.
Three candidates were angling to replace DeFelice weeks before he left the post.
One of the candidates, Vice Chairman Mike Cibik, will become acting chairman, according to party bylaws that require him to call an election within 30 days.
Cibik on Friday said he would notify the party's ward leaders Saturday that the election will be held at 7 p.m. Monday at the United Republican Club in Kensington.
DeFelice, in a letter Friday to the ward leaders, said he would be "pursuing other opportunities that would preclude me from continuing" as party chairman. He has declined to comment on those opportunities.
Michael Meehan, the party's longtime general counsel, pointed toward Trump.
"He indicated he has some type of job with the Trump administration," said Meehan, who is also a candidate for chairman. "I don't know the exact job or title. I assume it will be in the Philadelphia area."
Joe McColgan, a former candidate for the U.S. House and City Council, is the third candidate for chairman. His brother-in-law Val DiGiorgio became chairman of the Pennsylvania Republican Party in February.
DeFelice, who served as the party's executive director before taking over as chairman in February 2016, praised the ward leaders for "pushing that boulder up the hill" in a city where Democrats hold a 7-1 voter registration advantage over Republicans.
"We must support our president and elected Republican leaders and remain that loyal opposition and speak truth to power in the face of 60-plus years of Democratic rule," DeFelice wrote about Philadelphia.
The battle to be chairman could reopen some old wounds in the party, which went through a civil war of sorts between the old guard, like Meehan, and a group that called itself "the Loyal Opposition," which started pushing in 2009 to be more politically competitive.
Cibik, leader of the Fifth Ward, was part of the Loyal Opposition, as was DeFelice.