Amir H H Sheikh Tamim bin Hamad Al Thani attended the inauguration ceremony of President Recep Tayyip Erdogan for a new presidential term as the first President of the Turkish Republic after the new constitutional amendment.
Erdogan would become both the head of state and government, with the prime minister's post abolished.
Hours later, Erdogan announced the make-up a new streamlined cabinet which included his son-in-law as finance minister.
Erdogan´s supporters see the changes as just reward for a leader who has put Islamic values at the core of public life, championed the pious working classes and overseen years of strong economic growth.
The Turkish lira lost 3.5 percent in value on the news to trade at 4.73 lira to the dollar.
"We are leaving behind the system that has in the past cost our country a heavy price in political and economic chaos", Erdogan said in an address late on Monday.
Reuters adds: After taking the oath of office in parliament, he addressed worldwide leaders gathered at the presidential palace in Ankara.
He argued that the new structure would bring stability and efficiency and said, "is not forced but rather a sagacious choice that history has led us to".
The lira has been battered by concern about Erdogan's drive for lower interest rates and by comments in May that he planned to take greater control of the economy after the election, which he won on June 24. Erdogan's restructuring is the most significant adjustment of the country's political system since the formal establishment of modern Turkey. The inauguration ceremony, which was held in the Presidential Compound Monday evening, was attended by a number of heads of states and governments, representatives of heads of states, ministers, heads of parliaments of some countries and representatives of global organisations.
Erdogan referred to the principles of Mustafa Kemal Ataturk, the founder of the modern Turkish Republic.More news: At least 21 dead as tourist boat sinks off Thailand
After winning 52.9 percent of the vote in Turkey's presidential election two weeks ago, Erdogan was granted the ability to call additional elections, appoint judges without parliamentary approval, dissolve Parliament, and issue decrees that had previously been reserved for states of emergency.
"Most powers will be concentrated in his hands, there will no longer be a prime minister, and nearly none of the checks and balances of liberal democracies will be present".
European leaders and organisations have regularly clashed with Turkey over its involvement in the war in Syria, human rights and other issues.
Russian Prime Minister Dmitry Medvedev was present, in a new sign of the warm ties between Ankara and Moscow, as was Venezuelan President Nicolas Maduro, regarded with disdain by Washington but an ally of Erdogan.
In the aftermath of the 2016 coup, Turkey, a member of the North Atlantic Treaty Organisation military alliance and still nominally a candidate to join the European Union, has detained some 160,000 people, jailed journalists and shut down dozens of media outlets.
The new government faces immediate economic challenges.
In a speech on Saturday, Erdogan said he would tackle high-interest rates, inflation and a wide current account deficit. It then briefly dropped more than 1 percent after a decree removed a clause stipulating a five-year term for the central bank governor.
"When you scrap the five-year term you remove this shield", he said.
"We are now adopting a model that is way beyond our 150-year-old pursuit of democracy and our 95-year-long experience of a republic", Erdogan said.