Erdogan last month narrowly won a referendum on sweeping consitutional changes to create a presidential system in Turkey with just over 51 percent of the vote.
Under the old system, the head of state had to sever ties with their political party and Erdogan had to leave the ruling Justice and Development Party (AKP) when he became president in August 2014 after more than a decade as premier.
The reforms permit the president to be a member of a political party, allowing Erdogan to return to the AKP which he co-founded in 2001 as a new Islamic-rooted force in Turkish politics and which has dominated the scene ever since.
Supporters of the changes say they will bring Turkey efficient governance but opponents fear they will set the country on the path to authoritarian rule.
'Erdogan to take leadership'
Erdogan was welcomed as a new member at a special ceremony at party headquarters in Ankara by hundreds of AKP officials.
He signed the paperwork to become a member to thunderous applause before a rendition of the national anthem, an AFP photographer said.
Erdogan had travelled to the ceremony from his palace in a convoy including at least two dozen black vehicles driving on closed roads and carried live by all television channels.
AKP spokesman Yasin Aktay said Erdogan will also likely be reinstalled as party chairman on May 21 at an extraordinary AKP congress.
"During this congress, there will be an election and we envisage that the president will be elected as party chairman," Aktay told reporters.
As AKP head, Erdogan would replace Prime Minister Binali Yildirim who is set to stay on as premier.
If confirmed, it would be the first time that the president will be both party chairman and head of state since the end of the presidency of Ismet Inonu, the successor and right-hand-man of Mustafa Kemal Ataturk, Turkey's modern founder.
Erdogan's 'fifth child'
He is keen to sharpen the party's performance ahead of polls scheduled for 2019 after the 'No' vote came out on top in key battlegrounds including Ankara and Istanbul in the April 16 referendum.
Although the AKP has won every election since 2002, in June 2015 it suffered a setback after losing its absolute majority in parliament before winning it back in November that year.
The new constitution envisages major changes including the abolition of the premier's post and giving the head of state power to appoint ministers.
But these changes will only come into force after elections scheduled for November 2019 and the party membership shift is one of the few measures to take effect before then.
Samim Akgonul, a researcher from the University of Strasbourg, said Erdogan's return to the AKP would give him a "huge advantage".
By taking over the party, Erdogan would also be able to exert control over the rival personalities and different factions within the AKP.
"Erdogan wants to be master of the party de-jure and not only de-facto so his decisions... on appointments are not questioned," Akgonul added.
Erdogan co-founded the AKP along with other conservative heavyweights, including his predecessor Abdullah Gul who has yet to return to the party following his 2007-2014 presidency.
There was speculation in the Turkish media about whether Gul would attend the ceremony but Aktay said special invitations had not been made.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)