Armed with an emergency fund of more than 2 billion euros (£1.80 billion), the European Commission wants to strike deals with up to six drugmakers for their vaccines for their 450 million citizens against the coronavirus that has killed 674,000 people worldwide.
The Commission said the aim of the talks with Sanofi was to clinch an advance purchase deal.
"The envisaged contract with Sanofi would provide for an option for all EU Member States to purchase the vaccine," the Commission said in a statement.
"It is envisaged that, once a vaccine has proven to be safe and effective against COVID-19, the Commission would have a contractual framework in place for the purchase of 300 million doses, on behalf of all EU member states."
A Commission spokesman said he could not comment on when a deal would be announced and the possible price for the vaccine, calling it a quite promising step towards an eventual agreement.
Sanofi is working on two vaccine projects including one in partnership with GlaxoSmithKline.
The companies said the doses would be manufactured in European countries including France, Belgium, Germany and Italy.
Sanofi is leading the clinical development of the vaccine and expects to start a trial by the end of this year.
Earlier this week, EU talks with Sanofi, Pfizer and Johnson & Johnson hit an impasse over price, payment method and potential liability costs, EU officials told Reuters.
Other pharmaceutical companies talking to the EU include France's Valneva, Moderna and biotech firms BioNTech and Germany's CureVac.
By Foo Yun Chee