Democratic Party nominee Lee Jae-myung will be retried on electoral violation charges, while the acting president has resigned and is expected to enter the race.

South Korea's conservative party on Saturday named its former labour minister as its candidate for June's snap election to replace former president Yoon Suk Yeol who was ousted over his martial law declaration.

South Korea's third acting leader in five months, Lee Ju-ho, is an understated labour economist and education bureaucrat thrust into managing high-stakes trade talks with the United States and a country reeling from political knife fights before a crucial election.