Tupou VI was formally crowned King of Tonga on Saturday before thousands of people including heads of state and dignitaries from around the world, capping a week steeped in traditional rites.
Because it is taboo for Tongans to touch their king's head, a retired Australian minister was flown in to perform the crowning which was televised.
The new king also becomes the 24th Tu'i Kanokupolu, an ancient Tongan title that pre-dates the monarchy by centuries.
Celebrations and ancient rituals leading up to the coronation began last Saturday with a Taumafa Kava, a traditional ceremony in which Tupou VI drank the mildly narcotic kava drink to confirm his title as king of Tonga.
Newly crowned King Tupou VI (R) leaves the Centenary Church in Nuku'alofa on July 4, 2015. Tupou VI was formally crowned King of Tonga on July 4 before thousands of people including heads of state and dignitaries from around the world, capping a week steeped in traditional rites. (AFP)
The historic rite, in which about 150 nobles, wearing traditional ta'ovala mats around their waists, sat in a circle to drink kava from coconut shells, launched seven days of street parties, black-tie balls, fashion shows and feasting before the king was crowned by Australian D'Arcy Wood.
"No Tongan citizen can do it as it is forbidden for a Tongan to touch the king's head," the 78-year-old retired Methodist minister said last week before flying to Tonga from his home near Melbourne.
Wood was born in Tonga when his father worked there in 1924 and met the new king when he was Tonga's High Commissioner to Australia in the 1990s.
Tongan King George Tupou VI (2nd R), accompanied by his wife Queen Nanasipau'u (R), is crowned during the coronation ceremony in Nuku'alofa on July 4, 2015.(AFP)
Tupou VI, 55, ascended to the throne following the death of his bachelor brother Tupou V, who died in 2012 after a six-year reign of major reforms that expanded democracy in the nation of about 110,000 people.
An estimated 15,000 people, mainly expatriate Tongans, flew in for the coronation, with the invited guests including Japan's Crown Prince Naruhito, his wife Princess Masako, and European royals Prince Georg von Habsburg from Hungary and Princess Marie-Therese von Hohenberg from Austria.
Tonga's monarchy can trace its history back 1,000 years and by the 13th century the nation wielded power and influence over surrounding islands, including Samoa, nearly 900 kilometres (560 miles) to the east.
Japanese Crown Prince Naruhito (C-L) and Crown Princess Masako (C, R) arrive at the coronation ceremony of Tongan King George Tupou VI in Nuku'alofa on July 4, 2015. (AP)
Tupou I, who converted to Christianity after coming under the influence of missionaries, was proclaimed king in 1845 after winning control of the monarchy from two other royal lines.
By 1900 the country had become a British protectorate and acquired its independence in 1970. It remains the only monarchy among South Pacific island nations.