Erdogan is to officially step down as prime minister on Thursday in favor Ahmet Davutoğlu and will then be sworn in as Turkey's 12th president.
Emphasizing the continuity of change at the top of government, he said: "What is happening today is not a mission change but merely a name change. This absolutely is not a parting. You should know this is an opening, a beginning, an inauguration and a milestone. I want you to understand it like that.
"Following the presidential swearing in ceremony he, Ahmet Davutoğlu, will be given the task of forming a cabinet. And the new cabinet will be in place on Friday."
The final stages of Erdoğan's term as head of Turkey's ruling AK Party ends when Foreign Minister Davutoğlu replaces him as party chairman.
Davutoğlu, a multilingual former academic and foreign policy expert, will become prime minister after Erdoğan is sworn in.
The extraordinary congress in Ankara Arena follows Erdoğan's presidential election victory on August 10. Under Turkish law, the president cannot be connected to a political party.
The victory consolidated his hold on power after an 11-year tenure as prime minister. He is widely expected to bolster the powers of the five-year presidency, turning it from a largely ceremonial role to a more hands-on position.