ATHENS, Greece (AP) — Stefanos Kasselakis, a businessman who burst into Greek politics over a year ago, said he was leaving left-wing Syriza, the country's main opposition party he had led, and forming his own.

Kasselakis announced he was leaving Syriza Friday after a two-day party congress refused to consider his leadership candidacy in a contest that will take place later this month.

Kasselakis, 36, has lived most of his life in the U.S. and only entered Greek politics in May 2023 as a candidate in a national election. Syriza, already the main opposition party, suffered a disastrous double defeat at elections held in May and June of that year. He unexpectedly entered the leadership contest to replace longtime leader Alexis Tsipras and triumphed in September 2023.

His main opponent and several of her supporters bolted the party in December 2023, forming a new organization, New Left. Many of the Syriza members who had supported Kasselakis soon soured on him, accusing him of not being a true leftist. Kasselakis did not endear himself with his confrontational style and open disdain for the elected party organs.

In September, Syriza's central committee ousted Kasselakis from his post after a motion of no confidence. He contested the legitimacy of the vote and was set to run in the leadership race but was stopped by the party's central committee.

Along with Kasselakis, four lawmakers also bolted the party Friday and Saturday. This has left Syriza with 31 lawmakers in the 300-member Greek parliament, equal with the socialist PASOK party.

Under Tsipras, Syriza had governed the country from 2015-2019. Recent opinion polls show party support back into single digits.