King Maha Vajiralongkorn, or Rama X, inherited the throne following the death of his father in October 2016.
A period of mourning meant the official ceremonies were delayed.
The coronation, which takes place from Saturday to Monday, is estimated to have cost more than £23m.
The Crown of Victory is almost seven times heavier than the British monarch’s
It is the first the country has seen in 69 years, since his father, the late King Bhumibol Adulyadej, was crowned in 1950.
It comes at a time of political uncertainty following an unresolved election battle marred by claims of corruption.
Despite this, many Thais are excited to see the first coronation in many of their lifetimes.
The ceremonies are steeped in tradition and are based on mixture of Buddhist and Hindu Brahmin rituals.
The first day rituals represent a symbolic transformation from the human to the divine for the monarch.
Before being officially crowned, the 66-year-old king had to undergo a purification ceremony.
Dressed in white, he sat under a canopied fountain that poured consecrated waters over his head.
For weeks leading up to the coronation, water has been collected from sources across Thailand between 11:52 and 12:38 – an auspicious time according to Thai astrology.
The king then changed into a full uniform to receive sacred waters on his hands in an anointment ritual.
Selected officials, including military junta chief Prayuth Chan-ocha, poured the waters from the eight directions of a compass.
Seated on the Bhadrapitha Throne under the Royal Nine-tiered Umbrella, he was then presented with royal regalia.
This included a wooden sceptre inlaid with gold, a precious stone-encrusted sword believed to have been found in a lake in northern Cambodia, slippers, and a whisk made from yak’s hair.
A tiered, gold crown encrusted with diamonds and precious stones is the centrepiece.
Officially known as the Crown of Victory, the headpiece weighs 7.3kg – almost seven times heavier than Queen Elizabeth II’s Imperial State Crown.
King Rama X lifted the crown onto his own head before issuing his first royal command.
The day continues with the newly-crowned king granting a “grand audience” to members of the royal family, the privy council, the cabinet and senior officials.
The coronation is estimated to have cost more than £23m
This is followed by a visit to the Temple of the Emerald Buddha, the most sacred space in Thailand.
King Rama X will also take up ceremonial residence at the Grand Palace in Bangkok.
In the following two days, the newly anointed monarch will take part in a procession around Bangkok and make public appearances on his balcony so the Thai people can pay their respects.
The coronation is exceptionally important in Thailand where kings have traditionally held a divine status.
Criticising the monarchy is forbidden and the country has some of the strictest lèse-majesté (do wrong to majesty) laws in the world.
The future plans of the new king are still unclear.
After inheriting the throne in 2016, he replaced some of his father’s loyalists with his own and surprised the ruling junta by requesting changes to the new constitution to give the king more executive decision-making powers.
On Wednesday, he announced his fourth marriage to a former flight attendant, and confirmed her appointment as Queen Suthida.
