They have agreed to double the number of French police patrolling a 150km stretch of coastline targeted by people-smuggling networks.
However, the Home Office did not say how many more officers would be deployed.
Announcing the news on Saturday, Ms Patel insisted the agreement “will make a difference” to migrant numbers.
She added: “In fact the joint agreement that I signed, which secured the joint intelligence operation, has made a difference – even in the last six months – we have seen that.
“So we know that the French authorities have stopped over 5,000 migrants from crossing into the United Kingdom, we’ve had hundreds of arrests and that’s because of the joint intelligence and communications that we share between both our authorities.
“This new package today that I have just signed with my French counterpart, the French interior minister, effectively doubles the number of police on the French beaches, it invests in more technologies and surveillance (…) and on top of that we are now sharing in terms of toughening up our border security.”
The Home Secretary said the number of migrants making the crossing had grown exponentially, in part due to good weather.
But, she went on: “We should not lose sight of the fact that illegal migration exists for one fundamental reason: that is because there are criminal gangs – people traffickers – facilitating this trade.”
On top of that, she said, the cost charged by people traffickers has gone down so “people are putting their lives at risk”.
The announcement was criticised by a charity as an “extraordinary mark of failure” akin to “rearranging the deckchairs on the Titanic”.
UK and France agree to make intelligence cell to tackle migrant crossings
Ms Patel and Mr Darmanin also agreed an enhanced package of surveillance technology, with drones, radar equipment, cameras and optronic binoculars.
It is hoped the equipment will help the French deploy officers to the right places to detect migrants and stop them before they start their journey.
The agreement also includes steps to support migrants into accommodation in France, and measures to increase border security at ports in the north and west of the country.
It builds on measures previously agreed which the Home Office said had seen the proportion of crossings intercepted and stopped rise from 41 per cent last year to 60 per cent in recent weeks.
Despite deteriorating weather conditions, the UK’s Border Force has continued to deal with migrants making the dangerous trip from northern France.
The number crossing aboard small boats has rocketed this year, with more than 8,000 reaching the UK – compared with 1,835 in 2019, according to data analysed by the PA news agency.
This is despite the Home Secretary’s vow last year to make such journeys an “infrequent phenomenon”.
A recent report chronicled nearly 300 border-related deaths in and around the English Channel since 1999.
Written by Mael Galisson, from Gisti, a legal service for asylum seekers in France, it described the evolution of border security in and around the Dover Strait as a “history of death”.
It claimed responses to the migrant crisis have become increasingly militarised, forcing people to resort to more dangerous routes.
Bella Sankey, director of humanitarian charity Detention Action, said: “It is an extraordinary mark of failure that the Home Secretary is announcing with such fanfare that she is rearranging the deckchairs on the Titanic.
“No amount of massaging the numbers masks her refusal to take the sensible step of creating a safe and legal route to the UK from northern France, thereby preventing crossings and child deaths.
“Instead she throws taxpayers’ money away on more of the same measures that stand no chance of having a significant impact on this dangerous state of affairs.”
— to www.standard.co.uk