See main article: 2021 Open de Rennes.
Antonio Šančić and Tristan-Samuel Weissborn were the defending champions[1] but chose not to defend their title.
Bart Stevens and Tim van Rijthoven won the title after defeating Marek Gengel and Tomáš Macháč 6–7(2–7), 7–5, [10–3] in the final.