Harald, a reformer who spent more than three decades on the throne after gradually emerging from the shadow of his popular and charismatic father, died at a time of multiple crises for the Norwegian royal family.
Amid tight security, tens of thousands of people lined the streets to watch the funeral cortege move slowly towards Oslo's Lutheran Cathedral.
Its progress was punctuated by the sound of cannons being fired from the nearby Akershus Fortress.
Mourners, some of them wearing their regional costumes, fell silent as the coffin passed by.
Dignitaries processing on foot behind the coffin included Prince William, Japan's Crown Prince, the kings of Denmark, the Netherlands, Sweden and Spain, the presidents of Germany and Finland, France's prime minister and Ukrainian President Volodymyr Zelenskiy.
Representing the United States was Allison Hooker, Under Secretary of State for Political Affairs, the Norwegian government said.
Zelenskiy, who had held talks on his country's war with Russia late on Tuesday with Norway's prime minister, was applauded by the crowds when he later left the cathedral following the funeral service.
Harald was a popular monarch, widely praised by Norwegians for his inclusiveness, a view much in evidence on Wednesday.
"We lost our king. It's a very special day. And I think it's a special thing to be a part of," Adrian Soendergaard, 21, told Reuters as he watched the procession pass by.
Arve Stallvik, 56, a businessman, agreed: "(Harald) was very popular. I think everyone liked him so it was a moment for the history".
Hedda Michaelsen Mehlum, 23, said she thought the royal family remained very important for Norwegians, adding: "They do a great job representing Norway."
Hundreds of thousands of Norwegians had already paid tribute to him by leaving flowers, candles and flags outside the Royal Palace during the 13-day period of mourning.
Queen Mette-Marit, 53, the commoner wife of Norway's new King Haakon VIII, travelled to the cathedral on Wednesday by car with Harald's widow Queen Sonja, 89.
Mette-Marit is recovering from a lung transplant she underwent in June.
Last week, she had to cancel plans to attend her husband's oath ceremony in parliament due to complications following her operation.
Her son, Marius Borg Hoiby, from a relationship before her marriage to Haakon, was at the funeral despite being under house arrest and wearing an ankle monitor after his conviction for rape and domestic violence.
He is appealing the sentence.
Hoiby was one of the pall-bearers during the transfer of Harald's coffin to the royal chapel on August 31, drawing criticism in some quarters in Norway and abroad.
After Wednesday's service, four F-35 fighter jets flew over the cathedral, with one of them breaking out to symbolically mark the king's passing.
A smaller procession, walking to the rhythm of Frederic Chopin's Funeral March, accompanied the coffin to the royal crypt at Akershus Fortress overlooking Oslo harbour.
There, Harald's coffin was placed in a sarcophagus, alongside those of his parents.
When Haakon emerged from the crypt, the mourning period formally ended and flags that had been flying at half-mast since Harald's death were fully raised again.
Church bells across Norway rang out for an hour.
Later, Haakon, Mette-Marit and other members of the royal family appeared on the balcony of the royal palace and waved to the crowd, who clapped and cheered.
According to a Norstat poll published on September 1, the first poll taken since Harald's death, public support in Norway for the monarchy remains strong despite its recent troubles, with 72 per cent saying they backed the institution.
