Lahyani started his career with Sfax RS. In 2003, Lahyani signed with
US Monastir. He won four consecutive national league titles with Monastir from 2019 to 2022. On 28 May, he scored a team-high 21 points on 6-9 shooting in the
2022 BAL Finals to help Monastir win its first-ever BAL championship. In August 2022, he joined
Smouha of the
Egyptian Basketball Super League, ending his 9-year tenure at Monastir. He returned to Monastir ahead of the
2023 FIBA Intercontinental Cup, in February 2023. In October 2023, Lahyani joined the Moroccan club
AS Salé in the
2023 Arab Club Basketball Championship. After the Arab Club Basketball Championship, Firas Lahyani went back to US Monastir and ends up winning the Championship title of the
Tunisian League 2023–2024 season. ==National team career==