Macron and UK Prime Minister Keir Starmer are also expected to discuss maintaining support for Ukraine and curbing undocumented cross-Channel immigration.
Ahead of the summit, which follows two days of events spanning pomp and politics, trade and culture, France and Britain announced their "defence relationship" will be "refreshed".
They will order more Storm Shadow cruise missiles -- long-range, air-launched weapons jointly developed by the allies -- while stepping up work on a replacement system.
The missiles have been shipped to Ukraine in significant numbers to help Kyiv in its war with Russia since 2022.
Starmer and Macron will also agree to deepen nuclear cooperation and "work more closely than ever before on nuclear deterrence", according to Britain's defence ministry.
A new declaration will for the first time state that the British and French deterrents are independent but can be coordinated, and that an "extreme threat to Europe" could "prompt a response by both nations", the ministry said.
- Threats 'multiplying' -
The partnerships -- to be developed under a refreshed Lancaster House agreement first struck in 2010 -- herald a new "entente industrielle", making "defence an engine for growth", it added.
"From war in Europe, to new nuclear risks and daily cyber-attacks -- the threats we face are multiplying," Starmer said in a statement.
"As close partners and NATO allies, the UK and France have a deep history of defence collaboration and today's agreements take our partnership to the next level.
"We stand ready to use our shared might to advance our joint capabilities -- equipping us for the decades to come while supporting thousands of UK jobs and keeping our people safe."
Late Wednesday, at a speech to London's financial community, Macron said the two countries were "stronger together".
Starmer and Macron will also on Thursday dial into a meeting of the so-called "coalition of the willing" on Ukraine.
Britain and France are spearheading talks among the 30-nation coalition on how to support a possible ceasefire in Ukraine, including potentially deploying peacekeeping forces.
Starmer's office said this week that the call would "discuss stepping up support for Ukraine and further increasing pressure on Russia".
They will speak with Ukrainian President Volodymyr Zelensky, German Chancellor Friedrich Merz and Italian Prime Minister Giorgia Meloni, according to the French presidency.
- 'Innovative solutions' -
Macron's visit, the first by an EU head of state since Brexit, has been loaded with Anglo-French bonhomie and unifying rhetoric, alongside the usual pageantry of such occasions.
Macron and his wife Brigitte received a particularly warm welcome Tuesday from the Francophile King Charles III and Queen Camilla.
The pair toasted a new "entente amicale" at a lavish state banquet at Windsor Castle, hailing the importance of cross-Channel relations amid various emergent threats.
Wednesday saw the French president's visit turn to politics, with a Downing Street meeting with Starmer focused on migrant small boat crossings -- a potent political issue in Britain.
It is set to feature again at Thursday's summit.
Downing Street said the two leaders had "agreed on the need to go further and make progress on new and innovative solutions, including a new deterrent to break the business model" of cross-Channel people smugglers.
Macron also met with Anglo-French business representatives during the visit, while joining Starmer at the British Museum to formally announce a landmark cultural exchange.
France will loan the famous Bayeux Tapestry, depicting the 1066 Norman conquest of England, to the British Museum for 10 months from September 2026.
In return, London will lend French museums the collection from the Anglo-Saxon Sutton Hoo site, one of England's most important archaeological sites, as well as other medieval "treasures".
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