Atromitos On 28 November 2017, Mandas made his professional debut in
Greek Cup against
Sparta. On 30 September 2019, he signed a contract extension until the summer of 2022, with a buy-out clause of €2,000,000.
OFI On 31 January 2022,
OFI officially announced the signing of Mandas until the summer of 2026.
Lazio On 1 September 2023, Mandas officially joined
Serie A club
Lazio for an undisclosed fee. On 11 March 2025, he signed a contract extension until the summer of 2029.
Bournemouth On 27 January 2026, Mandas signed with
Premier League club
Bournemouth on loan until the end of the season. ==International career==