Born in Athens,[1][2] Katseris started playing football in the Greek amateur leagues,[3] before joining Eccellenza side Pavia in 2019, aged 18.
[2] Following a successful trial with Serie C side Catanzaro,[7] Katseris officially joined the club on a free transfer on 19 August 2022, signing a three-year professional contract.
[8][9] He made his professional debut on 8 October 2022, coming on as a second-half substitute in a 4–0 league win over Fidelis Andria.
[11] He scored one goal and three assists in 18 matches during his first season with the club, helping Catanzaro win automatic promotion to the Serie B.
[13][14] On 23 January 2024, Katseris joined Ligue 1 side Lorient for an undisclosed fee,[15][16] reported to be in the region of €2.4 million, plus €600.000 in add-ons,[17] signing a four-year-and-a-half contract with the French club.