Official SNCF Station Lockers ('Consignes Automatiques')
Five Paris terminals—Gare du Nord (Level -1 near car rentals), Gare de Lyon (Hall 3 exit Rue de Bercy), Gare Montparnasse (Hall 1 Level +1), Gare de l'Est (Level -1 near bakery), and Gare d'Austerlitz—plus Lyon Part-Dieu, Marseille Saint-Charles, Nice-Ville, Strasbourg, and Bordeaux Saint-Jean provide secure, X-ray screened lockers for €5.50 to €9.50 per 24 hours.
Hotel Holds & Verified Shop Networks
Nearly every French hotel will gladly hold your bags in their 'bagagerie' before check-in and after check-out at no charge. If sightseeing around Le Marais, Montmartre, or Vieux Nice far from a train station, use Nannybag or Bounce (€6/bag/day).
Official sources & further reading
Rules, prices and schedules change. Confirm details here before you travel: