They both were born citizens Athens, and they both were fated to become part of each other’s lives.
During the time that they lived, the city of Athens was under the command of the two sons of the previous tyrant, who too were tyrants themselves. Even though the term “tyrant” was different from what is today, they both were growing increasingly unpopular once Hipparchus (brother of the ruler and minister of culture) started to abuse the power of his position.
Among one of these actions, it was one that affected directly Harmodius. That would happen because Hipparchus would have feelings for him, but Harmodius would reject him. After this, Hipparchus, as a revenge, would call Harmodius sister to participate in a religious event, but would chase her out of the city under the accusation that she was not a virgin, and has disgraced the ritual for doing so. Such a scene has disgraced Harmodius family.
Eventually, Harmodius and Aristogeiton would become lovers, and they would discover a common disliking for the tyrants. In this, the two would conspire and would hatch a plan to destroy these two.
The plot was to be carried with hidden daggers during a great ceremony in which both of the tyrants would be present. The plan was to use the crowd to approach their targets with their daggers, stab them to death, and then merge back to the crowd and leave before the guards could organize themselves.
However, the plan went wrong as the lovers thought that they had been betrayed, and they had to rush with their plan. They were able to kill Hipparchus, but the spearmen came to the aid Hippias (the true ruler) before they could complete the plan. The lovers and their co-conspirators ran, but Harmodius was killed on the spot, while Aristogeiton would later be captured and tortured to give the names of the co-cospirators, but died before he gave any name.
After this, Hippias became paranoid, and increased his tyranny, causing a great dissatisfaction from the people, and he would later be overthrow.
The memory of the two lovers resisted, and they became known as the first tyrannicides.