The multi-year agreement calls for a 40% increase in the number of French officers patrolling French beaches with British funding over the following five months.
There is pressure on the new prime minister Rishi Sunak and interior minister Suella Braverman to do more to stop the flow after more than 40,000 people have already crossed the Channel to Britain this year, up from 28,526 last year.
As the government came under fire for the conditions at a crowded migrant processing centre in southern England last month, Braverman declared that Britain was under attack.
"It is in the interests of both the UK and French governments to work together to solve this complex problem," Braverman said after meeting French interior minister Gerald Darmanin in Paris.
In recent years, relations between Britain and France had deteriorated, first under Boris Johnson, who oversaw the UK's exit from the European Union, and later when Liz Truss, Sunak's predecessor, questioned whether French President Emmanuel Macron was a friend or foe.
Sunak met with Macron last week at the COP27 climate summit.
"I'm confident that we can get the numbers down but I also want to be honest with people that it isn't a single thing that will magically solve this. We can't do it overnight," Sunak said after arriving in Bali for the G20 summit.
Denis MacShane, a former British minister for Europe, expressed scepticism, telling Reuters that the additional funds were unlikely to make a significant difference given the hundreds of miles of coastline that need to be patrolled.
(With inputs from Reuters)
