Macron and Prime Minister Keir Starmer will also try to advance plans for a post-ceasefire security force for Ukraine, despite apparent US indifference to the idea and Russia's refusal to halt the onslaught on its neighbour.
Macron's three-day visit, at the invitation of King Charles III, is the first state visit to the UK by a European Union head of state since Brexit, and a symbol of the British government's desire to reset relations with the bloc that the UK acrimoniously left in 2020.
"The United Kingdom is a strategic partner, an ally, a friend," Macron wrote on X, in a marked change of tone from the years of wrangling over Brexit.
"Our bond is longstanding, forged by history and strengthened by trust."
The president and his wife, Brigitte Macron, were greeted on Tuesday on a red carpet at London's RAF Northolt air base by the Prince and Princess of Wales.
They were met in Windsor, west of London, by King Charles and Queen Camilla.
A military band played the French and British national anthems as all four set out for the royal residence of Windsor Castle in horse-drawn carriages, through streets bedecked in Union Jacks and French tricolour flags.
Later, the King and Queen will host a state banquet for their guests.
The British royals made a state visit to France in September 2023.
The monarch will make a broad appeal to international co-operation at the banquet, saying Britain and France "face a multitude of complex threats" that "know no borders" - and that "no fortress can protect us against them".
Macron will address both houses of Britain's parliament before sitting down for talks with Starmer on migration, defence and investment.
At a UK-France summit on Thursday, senior government officials from the two countries will discuss small-boat crossings, a thorny issue for successive governments on both sides of the English Channel.
Britain receives fewer asylum-seekers than Mediterranean European countries, but thousands of migrants each year use northern France as a launching point to reach the UK, either by stowing away in trucks or - after a clampdown on that route - in small boats across one of the world's busiest shipping lanes.
Starmer, whose centre-left government was elected a year ago, has pledged to " smash the gangs " behind organised people-smuggling.
Starmer and Macron have worked closely together to rally support for Ukraine, with Britain and France leading efforts to form an international peacekeeping force for Ukraine to reinforce a future ceasefire with European troops and equipment and US security guarantees.
US President Donald Trump has shown little enthusiasm for the idea, however, and a ceasefire remains elusive.
