Lagardère entered exclusive negotiations with Cosmopolitan owner Hearst on 31 December.
Titles in Hachette’s international (non-French) portfolio include British women’s magazines Red, Sugar and Inside Soap.
Hachette's portfolio of 80 magazines in France, which includes Elle and Psychologies, will continue to be owned by Lagardère, but published internationally by Hearst under licence.
Around the world there are currently 43 editions of Elle, considered the jewel in Hachette’s crown, and 12 editions of Psychologies.
The proposed all-cash deal has been valued in the region of £600m, although firm details about what has been described as a "very complex international sale," have yet to be revealed.
Lagardère and Hearst are expected to make internal announcements in the coming days and issue a joint external statement before the end of January. The two companies already have some existing international partnerships in place, most notably three joint-ventures which publish Marie Claire in Italy, China and Russia.
An official Lagardère spokesman said: "We shall not express ourselves before the term of the negotiation."
Hearst wholly owns the UK's National Magazine Company, publisher of a range of lifestyle titles, including Harpers Bazaar, Country Living, Good Housekeeping, Reveal and Esquire.
Hachette has a series of wholly owned or joint-venture publishing interests in addition to France, the UK and the US, including European operations in the Netherlands, Italy and Greece, and Asian partnerships in China, Hong Kong, South Korea, Japan and Taiwan.
Hachette’s local market partners have been in discussions with Lagardère Active representatives for the past two weeks, and many are travelling to Paris this week in the hope of finalising what they are calling "phase one" of the deal.
The multi-market deal is expected to take up to six months to finalise. Despite the onset of digital media and fragmentation of the media landscape, there remains a possibility that UK regulator the OFT could decide to investigate how the merger affects the marketplace and issue an invitation to comment to all interested parties.
This process could feasibly be repeated by regulators in many of the individual markets where Hachette and Hearst already have a notable presence.
At the same time, the European Commission could also decide to examine the implications of the deal separately.
Elsewhere, discussions are also being held between Hearst, Lagardère and third-party publishers in a number of local markets where partnerships are already established. Hachette currently publishes titles with Shkulev/InterMediaGroup in Russia, while Hearst partners with Dutch publisher Sanoma in the same country.
In the UK, the deal promises to ignite a fascinating battle by pitting the women’s portfolios of a newly combined Hachette and NatMags operation against rivals Condé Nast (Vogue, Glamour and EasyLiving), and IPC (Woman & Home, Marie Claire, InStyle).
Founded by American press magnate William Hearst in 1887, Hearst is widely recognised as leading the way in international publishing, currently with 61 editions of Cosmopolitan.