On 31 January 2020, Onana joined Lille from Leixões.[3] Onana made his professional debut with Lille in a 2–1 Ligue 1 loss to Marseille on 16 February 2020.[4] In August 2020, he joined Belgian club Mouscron along with some Lille players on loan,[5] where he received a red card in a Division A match defeat to Kortrijk on 13 September.[6]
On 30 August 2021, Onana moved to Ligue 1 club Bordeaux on a five-year contract.[7] On 1 September 2022, he signed for his former club Lille's rivals Lens on a five-year contract.[8] He made his first appearance with Lens on 4 September 2022 against Reims.
On 11 December 2023, it was officially announced that Onana has been excluded from the Beşiktaş squad along with Vincent Aboubakar, Valentin Rosier, Rachid Ghezzal and Eric Bailly due to poor performance and incompatibility within the team.[10] On 8 January 2024, Beşiktaş sent Onana on loan to Ligue 1 club Marseille until the end of the season, with an option to make the move permanent.[11]
In the early morning of 20 May 2024, Onana and OM teammate Faris Moumbagna were the victims of an armed robbery attempt while they were in their cars as they were leaving La Commanderie. Although neither were injured, two bullet holes were found on the driver's door on one of the vehicles.[14]
He is not related to André Onana despite sharing same surname.