Average temperatures between 1960 and 2024 have increased by 2.5 degrees Celsius (4.5 Fahrenheit) in the Mediterranean country, the observatory said on its meteo.gr website.
Three of the four warmest July temperatures of the past 80 years have been recorded in the last four years, it said.
"According to preliminary meteorological data... July 2024 was the warmest on record for Greece," it said.
The figures exceeded the previous record, set in July 2012, by 0.3 degrees Celsius (0.54 Fahrenheit), the observatory said.
June in Greece had also been the warmest since 1960, the observatory said last month.
Scientists say climate change makes extreme weather events including heatwaves more likely, longer lasting and more intense.
Last month the European Union's climate monitor said July 21 was the hottest day ever registered globally -- only for the record to be broken again the following day.
The Copernicus Climate Change Service (C3S) said the global average surface air temperature of 17.09 degrees Celsius (62.7 degrees Fahrenheit) on July 21 was the warmest in their data going back to 1940.
The following day, the daily global average temperature inched up a further 0.6 degrees, to 17.15 Celsius (62.9 degrees Fahrenheit).
