- January 14: A passenger train travelling from Tripolis to Kalamata derailed in the region of Anemodouri in Megalopolis, Arkadia. All 13 passengers were in a good state of health. The derailing was most likely caused by the aging of the line, as according to OSE, the train speed did not exceed 28 kph.
- January 22: The return of Dimitris Avramopoulos to New Democracy was officially announced, after his meeting with Kostas Karamanlis at the party's central offices.
- February 22: Archbishop Christodoulos calls the Annan Plan for Cyprus "anti-Greek" and claims it will lead to the de-hellenisation of Cyprus.
- February 29: Aris defeat Olympiakos 73-70 to win the Greek basketball Cup for a record eighth time. The match lasted four hours as the referees demanded that all fans leave the stadium ten minutes from time.
- March 7: Costas Karamanlis is elected Greek Prime Minister over Giorgos Papandreou. Karamanlis' New Democracy Party receives 45.36% of the vote whereas Papandreou's PASOK receives 40.55%. The Communist Party KKE is third with a 5.90% share of the vote.
- May 3: Nikos Magitsis becomes the first Greek to climb Mt. Everest.
- May 23: Panathinaikos put an end to Olympiakos 7-year reign in the Greek league after their 1-0 win over Paniliakos. The green team, which had already conquered the Greek Cup with a 3-1 win over Olympiakos, completed a memorable domestic double.
- May 26: Akis Zikos becomes the first Greek to play in a Champions' League final. His club, AS Monaco, lose 3-0 to Porto.
- June 4: The Athens 2004 Olympic Flame started a journey from Ancient Olympia to Athens, during which it visited 26 states and 34 towns on all 5 continents.
- June 6: Ilisiakos win the play-off match against PAS Giannina with 3-1 and return to Division B' of the Greek Football Championship after a period of 32 years.
- June 12: The Greek National Football Team spoil Portugal's party at Euro 2004 by beating the host team 2-1.
- June 13: Sports journalist Manolis Mavromatis is elected to the European Parliament.
- June 16: Greece draws with Spain 1-1 (Angelos Charisteas) in their second game for Euro 2004.
- June 20: Greece qualify for the knockout stages of Euro 2004 despite losing 2-1 to Russia.
- June 25: The Greek National Football Team advances to the Euro 2004 semi final game after beating France 1-0.
- July 1 - The Greek National Football Team advances to the Euro 2004 final game after beating the Czech Republic 1-0 (silver goal, overtime).
- July 4 - The Greek National Football Team beats Portugal at the final game of Euro 2004 and is crowned European Champions.
- July 7: Gogo Tsiligiri breaks the Greek pole vault record with a jump of 4.47m
- August 4: Demis Nikolaidis becomes President of AEK at age 31.
- August 13: The opening Ceremony of the Athens Olympic Games takes place. Weightlifter Pyrros Dimas is the flag bearer for Greece.
- August 16: Nikos Siranidis and Thomas Bimis win the gold medal, the first for Greece in the Athens Olympic Games, in the 3m platform synchronized diving
- August 21: Sophia Bekatorou and Emilia Tsoulfa win the gold medal in the double handed dinghy (470) race at the Athens Olympic Games. Tasoula Kelesidou wins the silver medal (66.68) in discus throw, and 33-year-old Pyrros Dimas, the best ever Greek weightlifter, wins the bronze medal in the 85kgs category with 175+202.5 kgrs saying goodbye to competitions leaving his shoes in front of the barbell. In Nikea, 6.000 fans delaud him interrupting the medal ceremony for 10 minutes.
- August 21: Chrysopigi Devetzi sets a new Greek record in the triple jump with 15.32m., in the preliminaries.
- August 22: Fani Halkia sets a new Olympic record in the 400m hurdles semi-finals with 52.77.
- August 22: Demosthenes Tambakos wins the gold medal with 9,862 points in the rings copetition at the Athens Olympic Games
- August 23: 22-year-old Athanasia Tsoumeleka wins the gold medal (1:29.12) in the 20.000km walking race at the Athens Olympic Games.
- August 26: Fani Halkia wins gold in the 400m hurdles at the Athens Olympic Games.
- August 28: Elisavet Mystakidou wins the silver medal in the 67kgs of taekwondo after losing in the final from Chinese Wei Luo at the Athens Olympic Games.
- August 29: Alexandros Nikolaidis wins the silver medal in the 80kgs of taekwondo after losing in the final from Korean Sung Moon Dae at the Athens Olympic Games.
- August 29: The closing ceremonies are held for the 2004 Summer Olympic Games in Athens. Anna Vissi, Dionisis Savvopoulos, Marinella and other top Greek singers give memorable performances.
- September 11: A helicopter crashes into the Aegean Sea killing 16 persons. Among them were the Patriarch of Alexandria and three other bishops.
- September 17: Imprisoned members of the Revolutionary Organization 17 November go on hunger strike to protest the "harsh" conditions of their imprisonment.
- October 2: Costas Douvalidis makes the first world record for Greece, in the cadet category, with 13.22 in 110m hurdles at Petralia in Skopelos.
- October 6: An Athens Appeals Court convicts four members of the Revolutionary People's Struggle (ELA) for terrorist-related crimes.
- October 7: A bomb explodes at the Patriarchate of Constantinople damaging the church of St George
- October 14: Two F-16 aircraft of the Hellenic Airforce crash on Pelion mountains in thick fog.
- November 17: Theodoros Zagorakis becomes the first Greek football player to earn his 100th cap.
- November 23: In the match between Olympiakos and Deportivo La Coruna (1-0), Predrag Djordjevic breaks the record for most CL appearances by a "Greek" player (53) and most goals (nine).
- November 27: The relics of Saint Gregory Nazianzenus are returned to Constantinople by the Roman Catholic Church.