The surprise announcement came after an opposition coalition in the former British colony broke the ruling party's four-decade grip on power earlier this month.
The 72-year-old, who was elected for a third five-year term last December but by a wafer-thin margin, is expected to be replaced by his vice-president Danny Faure.
"After 12 years as president, the time has come to hand over the reins of power to a new leader.
A new leader who will take Seychelles to the next frontier of its development," Michel said in a nationally televised address.
Parti Lepep has been in power since a coup in 1977, a year after independence, and it had won a majority in every election since the return of multi-party politics in 1993.
Michel, who has served as president as well as head of government, also paid the price after last December's presidential elections, in which he was re-elected but with 50.15 percent, only 193 votes more than opposition leader Wavel Ramkalawan.
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