The first responders who helped preserve the Gothic masterpiece and some of those who subsequently restored it received a standing ovation after the Archbishop of Paris, Laurent Ulrich, struck the doors of Notre-Dame three times with his crozier before symbolically reopening the building.
"I stand before you to express the gratitude of the French nation, our gratitude to all those who saved, helped and rebuilt the cathedral," French President Emmanuel Macron said on Saturday.
Notre Dame has formally reopened its doors for the first time since a devastating fire in 2019 (AP PHOTO)
"Tonight we can together share joy and pride. Long live Notre-Dame de Paris, long live the Republic and long live France."
Minutes earlier, the cathedral's bells rang out and Macron welcomed guests including US President-elect Donald Trump.
Pope Francis said it was a day of "joy, celebration and praise". In a message read aloud, the pope hoped "the rebirth of this admirable church would constitute a prophetic sign of the renewal of the Church in France".
Notre-Dame has been meticulously restored, with a new spire and rib vaulting, its flying buttresses and carved stone gargoyles returned to their past glory and white stone and gold decorations shining brightly once again.
Getting Trump to attend, and organising a meeting between him and Ukraine's leader Volodymyr Zelenskiy at the Elysee Palace ahead of the Notre-Dame ceremony, was a coup for Macron as he faces a political crisis at home, after parliament ousted his prime minister.
US President-elect Donald Trump was seated next to French President Emmanuel Macron. (AP PHOTO)
Trump shook hands with Britain's Prince William and heads of state and government as he made his way to the front of the cathedral. He sat next to Macron in the front row.
Earlier, guests stood and applauded as Zelenskiy walked into the cathedral.
Tesla billionaire Elon Musk also attended, as did Italian Prime Minister Giorgia Meloni and former French presidents Francois Hollande and Nicolas Sarkozy.
Earlier, tourists snapped pictures with the restored building in the background as final preparations for the event went on inside.
Some Parisians were particularly thrilled.
More than $A1.4 billion was spent on the restoration of the universal monument. (AP PHOTO)
"What does Notre-Dame mean to me? This. Look, it's here," said careworker Pascal Tordeux, displaying a tattoo on his arm representing the cathedral. "It means everything."
On the evening of April 15, 2019, dismayed Parisians rushed to the scene and TV viewers worldwide watched horrified as the fire raged through the cathedral.
"The planet was shaken on that day," Macron said ahead of Saturday's event.
"The shock of the reopening will – I believe and I want to believe – be as strong as that of the fire, but it will be a shock of hope."
Visitors can now book a free ticket online, on the Cathedral's website. But on Saturday, the first day bookings could be made for the coming days, all tickets were gone, a message on the site said.
Group visits will be allowed next year and the Catholic Church expects the cathedral to welcome 15 million visitors each year.
Thousands of experts - from carpenters and stonemasons to stained glass window artists - worked around the clock for the last five years, using age-old methods to restore, repair or replace everything that was destroyed or damaged.
"Notre-Dame is more than a Parisian or French monument. It's also a universal monument," said historian Damien Berne.
Notre-Dame has been meticulously restored by thousands of craftsmen. (AP PHOTO)
The cathedral's first stone was laid in 1163, and construction continued for much of the next century, with major restoration and additions made in the 17th and 18th centuries.
Money poured in for the renovation from all over the world - more than 840 million euros ($A1.4 billion).
