King Charles said the partnership between the UK and France needed to grow "ever closer" in the face of "profound challenges", as he hosted Emmanuel Macron at a state banquet at Windsor Castle.
The King and French president dined with the Royal Family and some 160 guests, including Sir Mick Jagger and Sir Elton John - with English sparkling wine on the menu.
Macron and his wife Brigitte earlier had been given a ceremonial carriage procession through Windsor, accompanied by the King and Queen and the Prince and Princess of Wales, at the start of their state visit.
The three-day visit is the first by a French president since 2008, and the first by a European Union political leader since Brexit.
Macron told MPs and peers, in a speech in the Houses of Parliament, that the UK, France and Europe should reduce their "excessive dependence on China and the US".
"We want an open world. We want to co-operate, but not to depend," he said.
King Charles, speaking in French and English, described the deep cultural, political and historic ties between the two nations before turning to the need for co-operation in facing cross-border threats.
He warned of an uncertain world, with risks of "terrorism, organised crime and cyberattacks". And he spoke of efforts to tackle "irregular migration across the English Channel".
The King joked about the "rapprochement" in the banquet menu, designed by chef Raymond Blanc.
"This evening, we have drunk English sparkling wine made by a French champagne house. This would have been scarcely believable to at least some of our predecessors," he said.
There were also references to shared cultural figures - such as Monet painting scenes in London and footballer Thierry Henry scoring goals for Arsenal.
In response, Macron recalled the historical ties between the two countries and spoke about the Bayeux Tapestry returning to the UK, more than 900 years after its creation, with plans for it to be shown in the British Museum next year.
Macron said that the final parts of the tapestry being missing was a "powerful symbol", showing that "in the great mural of Franco-British history, the end is yet to be written - it is up to us to do it".
Sitting beside President Macron was the Princess of Wales, who spoke last week about the challenges facing people recovering from chemotherapy.
Her appearance at all the state visit events will be seen as another step in her gradual return to public life.
Catherine had been absent from the last couple of big ceremonial dinners, with the South Korean state banquet in November 2023 the last she attended.
State visits are a mix of pageantry and ceremony and politics and trade. There will be a UK-France summit at Downing Street on Thursday, hosted by Prime Minister Keir Starmer, where issues such as stopping illegal migration and support for Ukraine will be discussed.
Ahead of the banquet in St George's Hall there had been an official welcome, with military bands playing and an inspection of guards at Windsor Castle.
Brigitte Macron had blown kisses to the crowds as the horse-drawn carriages rattled through the town.
There were famous faces at the Windsor banquet, including Rolling Stones singer Sir Mick Jagger, actress Dame Kristin Scott-Thomas, Sir Elton John, First Dates star Fred Sirieux and former England goalkeeper Mary Earps, who sat next to Sir Keir Starmer.
Windsor Castle was used as the venue because Buckingham Palace is undergoing renovations.
The menu for the evening included a special cocktail called "l'entente", which combined British gin with lemon curd and French pastis, decorated with French cornflowers and English roses.
The starter was a selection of tender summer vegetables with sage, raw tomato and extra virgin olive oil dressing.
The main course was a supreme of Rhug Estate chicken with Norfolk asparagus and tarragon cream.
Iced blackcurrant-soaked sponge with elderflower jelly.
The wine list was Domaine Evremond, Classic Cuvee, Edition I, NV; Corton-Charlemagne Grand Cru, Etienne Sauzet, 2022; Chateau Haut-Brion; 1er Grand Cru Classe Pessac-Leognan, 1996; Louis Roederer, Carte Blanche, NV.
Earlier in the day Macron addressed both Houses of Parliament, calling for the UK, France and their European neighbours to strengthen security and reduce their dependence on China and the US.
He praised the support from France and the UK for Ukraine, saying "we will fight until the very last minute" for a ceasefire to negotiate "sustainable peace".
On the conflict in the Middle East, Macron called for "a ceasefire in Gaza, without any condition", and added "working together" to recognise a Palestinian state is the "only path to peace".
There would also be "tangible results" from joint efforts to stop illegal migration across the Channel.
The French president praised the legacy of the late Queen Elizabeth II - and on Wednesday he will visit her tomb in Windsor. He will also visit a horse that he gave to late Queen, as a gift for her Platinum Jubilee.
Across the three-day visit, there will be a message of building relations between the two allies, in diplomacy, defence and trade, at a time of uncertainty in international relations.
The UK government has spoken of wanting to "reset" post-Brexit relations with European neighbours with the French state visit part of that process.
