A royal command promulgating the 279-section constitution was published on the website of the Royal Gazette Thursday.
In a rare ceremony not seen in almost 50 years, His Majesty the King signed the country's supreme law at the Ananta Samakhom Throne Hall in Bangkok at 3.11pm in front of a grand congregation.
Those present included privy councillors, cabinet ministers, members of the National Legislative Assembly, the Constitution Drafting Committee, the presidents of the Supreme Court and independent organisations, high-ranking officials and foreign diplomats.
A similar ceremony was held on June 20, 1968 when the late King Bhumibol Adulyadej signed the country's 8th constitution.
The King signed each of the three handwritten copies of the constitution in the form of the Samud Thai -- a long, narrow, folding book made up of paper sheets bound together which is traditionally used to inscribe important documents including the constitution, the country's supreme law.
All three books were then given to Prime Minister Prayut Chan-o-cha. Officials subsequently added the royal stamp and put them on three separate gold trays.
The three copies will now be kept separately with one at parliament, one at the Office of His Majesty's Principal Private Secretary, and the third at the Bureau of Royal Scribe and Royal Decorations under the secretariat of the cabinet.
During the ceremony an official from the the bureau read a preamble of the new constitution.
According to the preamble, Thailand has adhered to a democratic government with the King as head of state since King Rama VII endorsed the country's first constitution in 1932.
However, several charters have been abrogated, amended or new ones drawn up to properly regulate national administration, it read.
National administration has not always been stable or orderly due to a range of problems and disputes, some of which were constitutional crises with no clear solution, it added.
These problems resulted partly from the fact that the country's leaders disregarded or disobeyed the rule of law, engaged in corruption or abuse of power, or lacked a sense of accountability towards the country and the people, which in turn rendered law enforcement ineffective, according to the preamble.
Some of the problems stemmed from governing rules not best suited to the country's special circumstances, attaching importance to the form rather than the fundamental principles of democracy, it read.
These rules could not always be applied effectively to deal with people's actions during periods of crisis, especially for situations that lacked precedent, it added.
Under the interim constitution, a Constitution Drafting Committee was established to draw up the new charter and other important legislation to create mechanisms for stronger governance.
Certain organisations' duties and power has now been restructured, a move also aimed at properly shaping the relationship between the legislative and executive branches.
The new charter allows the courts of justice and independent oversight bodies to carry out their work more efficiently and play a role in preventing or resolving crises, according to the preamble.
It also provides clearer and more comprehensive protection of the public's rights and freedom, it said, adding that the rules in this area have been designed protect the majority.
The constitution also puts in place rigorous mechanisms to prevent and scrutinise corruption and wrongdoing in order to keep those who lack integrity and good governance from running the country or abusing their authority, it said.
Meanwhile, the new constitution includes measures to more efficiently manage and handle national crises.
The preamble also stressed that it is important for all parties to work together, pursue unity and harmony, and reduce conflict for the sake of peace and happiness.
In order to achieve these goals it is necessary for people in all sectors to work with state agencies under the Pracharath (people-state partnership) approach and under the democratic system, it said.
Governing traditions fitting to the country's circumstances, social identity, moral integrity, human rights principles and good governance must also be respected, it added.
After the draft passed the referendum in August, it was submitted to the King for approval. Cabinet ministers said the King had made some suggestions about the sections involving royal prerogatives and the changes had nothing to do with the rights and liberties of the people.
Changes were made to six sections of the draft constitution after it passed the referendum in August.
The changes were not known until Thursday, when the final constitution came into effect.
The website of the Royal Gazette published it in full.
Key changes include Section 5, the so-called "crisis management clause".
In the referendum version, this provides that in cases where no provision applies to any case, a meeting will be convened among the heads of the Constitutional Court, Senate, Supreme Court, Supreme Administrative Court and independent organisations, as well as the speakers of the House, opposition leaders and the prime minister.
The decision of the joint meeting shall be deemed final and binding on all state bodies.
The new charter eliminates such clauses and changes it back to the text of the 2007 charter, which says: "Whenever no provision under this Constitution is applicable to any case, it shall be decided in accordance with the constitutional convention in the democratic regime of government with the King as Head of State".
The second change involves Section 16 on the Regent.
The referendum version requires the King to appoint the Regent when he is not in the kingdom or is unable to perform his duties as expected.
The new constitution dropped that requirement and states the King may or may not appoint the Regent in such cases. He may also name a person or a group of persons as the Regent.
Sections 17 and 18 did away with the requirement that the Privy Council name the Regent and send it to parliament for approval when the King is not in the kingdom or cannot perform his duties.
The new constitution requires the Privy Council propose only the names of a person or group of persons that His Majesty has previously chosen as the Regent for parliamentary approval.