Turkey’s President on Tuesday rejoined the ruling party he co-founded in a step on his path toward solidifying his grip on power, following his narrow victory in last month’s referendum.

Most of the constitutional changes ushering in a presidential system, approved in the April 16 referendum, will take effect after the November 2019 election. But an amendment that reverses a requirement for the President to be non-partisan and cut ties with their party come into effect immediately, allowing President Recep Tayyip Erdogan to return to the Islamic-rooted Justice and Development Party, or AKP.

The party is expected to re-elect Mr. Erdogan as its chairman at an extraordinary congress on May 21.

Mr. Erdogan symbolically signed a membership form in an emotional ceremony at the AKP’s headquarters, where some party members were seen weeping. Erdogan was also seen wiping his eyes with a handkerchief.

“I am today returning to my home, my love, my passion,” Mr. Erdogan said. “This yearning [for my party] is ending after 979 days.”

Mr. Erdogan, who was prime minister between 2003 and 2014, was forced to resign from the AKP when he became president. The father of four continued to lead the party he once described it as his fifth child from behind the scenes. For example, Mr. Erdogan had the final say on the list of candidates running for parliamentary seats.

The changes formalize a de-facto situation but also allow him to maintain a tighter grip on the party. Recent political history saw former Presidents Turgut Ozal and Suleyman Demirel lose control over their parties, after they become heads of state and left their parties.

“In effect, the existing, de-facto situation will become legal,” said Ozgur Unluhisarcikli, director of the Ankara office of the German Marshall Fund of the United States.

“Erdogan attaches as much importance to controlling his party as he does the new presidential system,” Mr. Unluhisarcikli said. “Political parties play an important part in the Turkish political system and a leader who controls a party holding a majority controls many things.”

Mr. Erdogan arrived at the AKP headquarters in a 13-vehicle motorcade, the five-minute journey broadcast live on television channels.

“Welcome back to the home that you founded,” Mr. Yildirim said. “Today is a historic day for Turkish politics and its democracy.”

Mr. Yildirim reaffirmed that Mr. Erdogan would be nominated as chairman at the congress later this month.

Mr. Erdogan’s “yes” camp won the referendum with 51.4 % of the vote against 48.6 % for the “no” side, according to final results announced last week.

The main opposition party contested the outcome, citing irregularities, and is challenging the referendum at the European Court of Human Rights, following unsuccessful Turkish high court appeals.

During his speech on Tuesday, Mr. Erdogan said, however, that the European court has no jurisdiction over the referendum.

“It has no right to intervene in this country’s internal affairs concerning elections,” Mr. Erdogan said.

The vote switches Turkey’s system from a parliamentary one to a presidential system, abolishing the office of prime minister while enhancing the president’s powers.

Critics fears the change will lead to a one-man authoritarian rule with too few checks and balances. Mr. Erdogan and his supporters argue that a strong presidency will bring stability and more efficient government.