SEOUL, South Korea — A former North Korean diplomat who fled his embassy posting has become the first defector to run for South Korea’s Parliament, saying on Wednesday that he was motivated by Seoul’s forced repatriation of two North Korean fishermen who wanted to defect to the South.

“This was so wrong, even if they were criminals,” said the former diplomat, Thae Yong-ho, referring to the two North Koreans who were repatriated to the North in November after they were captured in waters off South Korea.

Mr. Thae was the No. 2 diplomat in the North Korean Embassy in London when he fled to South Korea with his wife and two sons​ in 2016​.

South Korea’s main conservative political opposition, the United Future Party, selected him to run in National Assembly elections in April.