The newest member of the royal family is the fourth wife of 66-year-old Vajiralongkorn, a deeply private monarch who spends a lot of his time overseas in Germany.
At least 150,000 people from all over the country were expected to greet their newly crowned king, first during a parade around old Bangkok on Sunday, then near the Grand Palace where the king will appear on the balcony on Monday.
The king held a grand audience with members of the royal family, the Privy Council and senior officials later in the afternoon at the Grand Palace.
Spectators all wearing yellow, the colour associated with the king, gathered from early morning along the 7 km (4 mile) route from the Grand Palace to three royal temples.
The crowning ritual was introduced from Europe to the Thai coronation ceremony during the reign of King Rama IV.
The procession, a triumph of traditional, golden splendour, was the King's first public appearance since he completed an elaborate set of coronation rituals on Saturday.
He later took his seat under the umbrella of state and was handed the Great Crown of Victory, a tiered gold 7.3-kilogram (16-pound) headpiece topped by a diamond from India. It symbolizes his royal powers, which include the right to intervene in government affairs.
"I shall continue, preserve and build upon the royal legacy and shall reign with righteousness for the benefit and happiness of the people forever", the king said as his first royal command.
Though Thailand has had a constitutional monarchy since 1932, when a revolution ended absolute rule by kings, the country's monarchs are regarded as nearly divine and have been seen as a unifying presence in a country that has seen regular bouts of political instability as it rotates between elected governments and military rule. But opposition politicians are seeking to push the army out of politics. It started around 5pm (1000 GMT) at the grand palace in Bangkok's old quarter as trumpets blared, soldiers shouted commands and cannons fired a 21-gun salute. "We have been shown the importance of this institution since we were young and how much the previous king had done for us". The rites are a combination of Hindu and Buddhist practices and go back centuries.
King Vajiralongkorn is the tenth monarch of the Chakri dynasty, which has reigned since 1782.
The coronation, costing around $31 million (€27.6 million), was broadcast on television, with subjects also able to watch it on LED screens sited outside the palace.
It is not yet clear how many people will qualify for the pardons. Numerous spectators wore yellow - a color associated with the monarchy. The king also received and wore five articles of the royal regalia from the chief Brahmin, signifying full kingship. Here, the officials and dignitaries pledge their allegiance to king and country.