The move, which has been widely reported for some time, was made official in a decree on February 28th and published on Thursday.
“Every driver of a motorised land vehicle, excluding mopeds, must possess an unused and immediately available breathlyzer,” said the decree, published in the official gazette (“Journal Officiel de la République Française”).
Transport ministry officials told The Local that the rule would apply equally to vehicles from outside France.
July and August are busy months on the French roads as millions of French people and tourists head for their holiday destinations.
A fine of €11 ($15) will be charged to anyone not carrying the breathalyzer kit, but police have been told to start fining only from November 1st.
The new law is the latest attempt to reduce France’s road accident rate.
Around 4,000 people died on French roads in 2011, a very slight improvement on the figure for the year before.
Drink driving is believed to be responsible for one in three road deaths.
The government hopes having a kit in the car will allow people to test themselves and to give them the means to test others if they suspect they are over the limit.
The legal blood alcohol limit in France is 0.5 grams per litre.
The single-use tests cost between €0.50 and €1.50 and manufacturers are rushing to produce enough to meet expected demand.
President Nicolas Sarkozy promised the measure in November in the hope of slashing drink driving, responsible for 31 percent of fatal road accidents.
Disposable breathalysers have been available in French bars and nightclubs since then.
New coaches have been equipped with breathalyser tests that prevent drivers starting the ignition since January 2010. The devices are to be installed in all coaches by the start of the 2015 school year.
A total of 3,970 people died on French roads in 2011, down barely 0.5 percent or 22 lives compared to 2010.
When Sarkozy came to power in 2007 he set the government the ambitious target of reducing annual road deaths to 3,000 by 2012.
The new breathalyzer requirement will be added to the existing rules compelling drivers to carry a warning triangle and a fluorescent safety vest. Failure to have these in the car can lead to a €90 fine.
More information is available, in French, on the website of the government road safety agency, Sécurité Routière.