The millions of euros France is offering would pay for equipment and training - and comes in addition to a 105 million euros European Union package that the E.U. Commission president announced earlier this month to help Tunisia tackle a big rise in migrant departures.
Perilous sea crossings, often on crowded, flimsy boats, have led to a terrible toll of drownings, as well as a big increase in migrant arrivals in Italy this year causing political ructions in Europe.
Last week's sinking of a boat carrying hundreds of migrants from Libya to Greece underscored the risks of the crossing.
Tunisian President Kais Saied has said his country will not be a border guard for Europe but he also announced a crackdown in February on sub-Saharan African migrants living in the country.
That crackdown, announced using language the African Union said was racialized, appeared to prompt an increase in migrant departures from Tunisia.
"Tunisia's role is not to be a coastguard, but we are working to minimize departures," said France's Darmanin.
He said he had also submitted to Tunisian authorities a list of people he wanted to return to Tunisia from France. He said Tunisia had asked France to be more flexible with visas for its citizens.
The number of migrants from Tunisia is also increasing as the country faces a bleak economy and a looming crisis in public finances.
The E.U. has also offered Tunisia around 1 billion euros to help state finances if it agrees to an International Monetary Fund program that includes cuts to subsidies and the restructuring of state-owned companies.