With the support of his family and the help of Spartans, he overthrew the rule of Hippias, the son of peisistratus. However, in the power vacuum after the collapse of the dictatorship, he faced the challenge of Isagoras. The latter took the lead and became a consul in 507-508; On the other hand, Cleisthenes's reform plan has won public support. When Isagoras saw this situation, he sought support from King Cleominis I of Sparta to exile Cleisthenes, and got a response. The latter sent a small army and reiterated the curse of Maion family in Arce, forcing Cleisthenes and his supporters into exile, while Isagoras seized power without competition. He tried to establish oligarchy and tried to dissolve parliament. This move was strongly resisted by the parliament and widely supported by the people of Athens. Isagoras and his staff were forced to flee to the Acropolis, where they were besieged for two days. They finally surrendered on the third day and handed over power. In this way, Cleisthenes was recalled, regained power and continued his democratic reform.
He first abolished four traditional tribes, because they originated from family relations and easily led to dictatorship. He divided Attica into 139 "autonomous regions" (δ? μο? ), divided into 30 "trittys" (each trittys contains about 3 autonomous regions) and 10 Phylai (the singular is Phyle, which can be translated as "tribe", but it is not accurate). Each gate consists of three "three zones", which come from the city (Asti, the periphery of Athens), the coast (Palalia) and the inland (Mesoggia). He also established a legislature that was decided by lottery, not based on nepotism or blood relationship. He reorganized the parliament (β ο υ λ η). When Solon was founded, there were 400 people, but he changed it to 500 people: each clan contributed ten people. The court system (Dikasteria, jury court) has been reorganized, and 200 to 5,000 people are selected to participate in the jury every day, of which each door can provide up to 500 people. The function of the 500-member parliament is to submit bills to the voters' assembly, which meets about 40 times a year to perform its duties. The proposed bill may be passed, rejected or sent back to parliament for amendment.
It seems that Cleisthenes also created the exile system of pottery tablets (first implemented in 487 BC), giving people the right to exile a citizen for ten years. At first, this system was designed to prevent the democratic system from being destroyed. For example, it was applied to a person who was ambitious to become a tyrant. However, citizens who were considered to have too much power soon became targets of exile, such as Xanthippus in 485/84. Under this system, the property of the exiled person will be preserved, but he himself is not allowed to enter the city-state when he is exiled.
Cleisthenes called these reforms "isonomia" rather than "democracy". But his life after the political reform has always been a mystery, and there is no existing ancient book record.