He was renowned for his love of military uniforms and a jet-setting lifestyle, but in his six-year reign Tupou managed to pave the way for democracy in the country of 100,000 people.
The body of the 63-year-old was placed on a massive wooden bier at noon (2300 GMT Monday) after lying in a casket in the throne room of his palace where locals had observed an overnight vigil.
Hundreds of men, all wearing black clothes and traditional woven ta'ovala mats around their waists, carried the bier some 300 metres (yards) to the royal tombs, some straining under the weight as the midday sun beat down.
The monarch's younger brother King Tupou VI, who will take over as head of state, and his wife Queen Nanasipau'u walked behind with other family members, many wearing mats which almost blanketed them to show their closeness to the deceased.
As the bells of the Free Wesleyan Church tolled, a 21-gun salute began and a military band led the procession on its stately journey watched by hundreds of Tongans lining the streets.
"It's very moving," said Tafolosa Bloomfield who wanted to witness the historic funeral procession, last seen in Tonga in 2006.
"We feel for the king. Despite all the political differences when it comes to the king and our culture, nothing else matters," she told AFP.
Daphne Manu, a Tongan visiting from the United States whose nephew was among the pallbearers, said the ceremony was overwhelming.
"That was amazing," she said, pointing out the crowds of men and women in traditional dress.
The royal palace, like most buildings in Tonga, was swathed in black and purple fabric to mark the death, with the island's devoutly Christian people praying and singing outside.
The funeral brought normal activities in the capital of Nuku'alofa to a standstill, with two public holidays seeing businesses closed.
"It's a major event that affects all Tongans," said Sandra Fifita, acting director of the Ministry of Tourism, as she wiped away her tears.
"He is our king and we have such respect for him as our king and our leader."
George Tupou V, who was not married, was the direct descendant of King Tupou I, who founded the dynasty in the middle of the 19th century.
He died in Hong Kong over a week ago and arrived back in Tonga Monday. The cause of death has not been released but he underwent treatment last year for cancer.
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 (500 miles) to the east.
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 only acquired its independence in 1970, becoming a member of the Commonwealth of Nations. It remains the only monarchy among South Pacific island nations.