S. Korea's ex-president Yoon leaves party ahead of snap election
The People Power Party (PPP) had been under pressure to expel Yoon ahead of the June 3 election, as polls showed it trailing the main opposition party.
"I am leaving the People Power Party today," Yoon, who is standing trial on criminal charges of insurrection, wrote on Facebook.
He urged voters to support his former labour minister Kim Moon-soo, the PPP's presidential candidate.
Kim shot to public prominence as the only cabinet member who refused to bow in apology for failing to prevent martial law.