Donis is a product of Panathinaikos' youth ranks. He promoted to the first team on July 1, 2012, signing a contract which keeps him in Panathinaikos until 2015. He made his debut at the 4–0 win against Proodeftiki for the Greek Cup. He made his championship debut at a game against Levadiakos on the 18th of December 2013, scoring his first goal with the team. On 15 February 2016, Panathinaikos officially announced the loan of Christos Donis to Swiss club Lugano until the end of the season, with a contract option to purchase him. The 21-year-old midfielder wοuld have his younger brother, Tasos, as a teammate. On 27 June 2016, after an unsuccessful semester with Lugano, his club officially announced his loan to the Superleague club PAS Giannina until the end of the 2016–17 season. On 29 November 2016, he scored the only goal in a 1–0 away Greek Cup win against Agrotikos Asteras, helping his club to proceed to the last 16. In January 2017 he was transferred to Iraklis, on loan. On 5 April 2017, he was the only scorer in a crucial 1–0 home win game against Levadiakos, sealing a crucial victory in his club effort to avoid relegation. On 9 April 2017, he scored for a consecutive game sealing a valuable 2–1 away win against his former club PAS Giannina in his club's constant effort to avoid relegation. On 30 April 2017, he helped his club to sealing a 2–2 away draw against Asteras Tripolis, with a wonderful free kick, concluded his exceptional performance in the second half of the 2016–17 season. Donis returned to Panathinaikos for the 2017–18 season. On 21 January 2018, he opened the score in a hammering 4–0 home win game against Kerkyra. It was his first goal with the club after almost four years. On 6 April 2019, he scored his first goal for the 2018–19 season was in the right place at the right time to convert an excellent pass from Italian striker Federico Macheda, as Panathinaikos moved to within five points of fifth-placed Arisafter claiming a solid 2–0 home win over the Thessaloniki club at the Olympic Stadium. On 12 January 2020, he scored his first goal for the 2019–20 season as he intercepted the ball from a poor clearance made by Panionios defender Domingues, and he surged forward before hitting a powerful diagonal shot past the helpless visiting goalkeeper Jérémy Malherbe to open the score in a 3–0 home win game against Panionios.
Personal life
Donis is the son of the former professional footballer and current manager of Panathinaikos, Giorgos Donis. His younger brother, Tasos, plays for French club Stade de Reims.
