As a player, Vlachos played for Olympiacos from 1989 to 1998, winning numerous titles. He was also a member of the Greece men's national water polo team. After his retirement, he became assistant coach of Olympiacos under coaches Dragan Matutinović, Zoltán Kásás and Veselin Đuho.[3] He became Olympiacos head coach in 2011, following a successful stint as head coach in Palaio Faliro. Under his guidance, Olympiacos won the 2017–18 LEN Champions League in Genoa, after a 9–7 win against home team Pro Recco in the final and completed a Triple Crown, winning the season's all available titles.[4][5] Besides the LEN Champions League and the Triple Crown, he has also coached Olympiacos to 10 consecutive Greek League titles (2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021, 2022) 9 Greek Cups (2013, 2014, 2015, 2016, 2018, 2019, 2020, 2021, 2022) and 7 domestic Doubles.[6]