The previous king, Bhumibol Adulyadej, ruled for 70 years, making him the longest-reigning monarch in the world when he died in 2016.
The coronation comes more than two years after Vajiralongkorn ascended the throne following the death of his father, the much beloved King Bhumibol.
On Sunday, there will be a 7-kilometer royal procession involving 343 men, in which the King will again be carried on his palanquin through nearby city streets to visit four important temples and allow the public to pay homage to him.
There, he will light the auspicious candle at 4:19 p.m. (9:19 GMT) - a time that court astrologers determined was propitious - while 80 Buddhist monks chant.
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.
Results from the election are due to be announced on 9 May, just three days after the end of the coronation ceremony.
The King was also offered the Royal Golden Plaque with inscription of his official title, the Royal Seal, the Sword of Victory, the Royal Scepter, the Royal Fan and Fly Whisk, and the Royal Slippers, among others.
The king will also reduce sentences for some prisoners, including those imprisoned for life, and commute inmates' death sentences to life. Though the royal family is nominally above politics, the king issued an election-eve message calling on Thais to vote for "good people" against those who create "chaos".
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The teenager is the king's son from his third marriage. His 86-year-old mother, known as Queen Sirikit, was granted a new official title of Queen Mother. Junta chief Prayut Chan-O-Cha, who seized power in a 2014 coup, took part in numerous key rituals, including the procession.
The high-reaching crown, which weighs 7.3 kg (16 lb) symbolizes the summit of Mount Meru, the Hindu god Indra's heavenly abode, and its weight represents the monarch's royal burden.
It was also during King Mongkut's coronation that foreigners were invited to witness coronation ceremonies for the first time, scholars said.
Briefly after his anointment on Saturday, he installed Queen Suthida, a former flight stewardess who later became deputy chief of his bodyguards unit.
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.
During the 18 months of his reign so far, King Vajiralongkorn has moved to consolidate the authority of the monarchy, including taking more direct control of the crown's vast wealth with the help of Thailand's military government. The rite, known as the Royal Purification Ceremony, took place amid music from drums, conch shells and other instruments. The King would grant new royal titles to royal family members, ride in the royal palanquin in the royal procession to receive people's good wishes on Sunday, and meet a public audience including members of global diplomatic corps on Monday.
Thailand has been run by an arch-royalist junta since 2014.