At a summit designed to rebuild ties after years of bickering over Brexit, British Prime Minister Rishi Sunak and French President Emmanuel Macron said the two sides had agreed to work more closely together.
"It is time for a new start," Macron said.
"Emmanuel and I share the same beliefs," Sunak said. "Criminal gangs should not get to decide who comes to our country. Within weeks of my coming into office, we agreed our largest ever small boats deal and today we've taken our cooperation to an unprecedented level to tackle this shared challenge."
Sunak has made stopping boat arrivals one of his five priorities after the number of migrants arriving on the south coast of England soared to more than 45,000 last year, up 500% in the last two years.
As part of the new deal, Britain will help fund a detention center in France while Paris will deploy more French personnel and enhanced technology to patrol its beaches. Officers from both countries will also look to work with countries along the routes favored by people traffickers.
The funding package will be paid in instalments, with the French also contributing significantly more funding, they said.
Sunak, who became Britain's prime minister in October, is hoping to capitalise on renewed goodwill with France and the wider European Union after he struck the Windsor Framework - a new agreement with the bloc aimed at fixing problems with Northern Ireland's post-Brexit trading arrangements.
Later this month, King Charles will also travel to France on his first state visit as monarch.