"All day we've just been having a wonderful time together, praising God, and loving each other and rejoicing," Callahan said.
Parishioners and others who've followed her theological career arrived at St. Paul's Sunday afternoon for her installation service.
They believe her election is well deserved.
"Dr. Callahan is a very lovely person; I like to hear her preach and I think she gives a very good message to everyone that she preached to," Iula Brown of Willow Grove, Pennsylvania said.
Dr. Callahan says the road to lead pastor has not been an easy one. Despite recent studies which say senior female pastors have doubled in the past 10 years, men are mostly elected to such positions. That didn't stop Dr. Callahan.
"I think it's an awesome thing. Traditionally, women weren't revered like the men have been, but God is always changing things," Deacon Daniel Cook said.
"Things are changing in the world, things are changing in the nation, things are changing in the church, so this is representation of that change here in Philadelphia," Callahan said.
Despite her historic rise, Dr. Callahan says there were moments she questioned if she'd ever get here, but her faith prevailed.
"I always trusted that the gift and the calling that God had given me would eventually be recognized, that people would be courageous and give me the opportunity to do what I believe God has called me to do," Callahan said.