Thae Yong-ho has become the first ever North Korean defector to win a constituency seat in South Korea, BBC reports.
Mr Thae was once North Korea's deputy ambassador to the UK, but defected in 2016 with his family, becoming the highest-ranking North Korean official to ever do so.
He was running as the opposition United Future Party's main candidate in the affluent district of Gangnam of Seoul.
He won by 58.4% and was seen crying after his victory was announced.
He said ahead of his victory that he hoped his running would send a message to the elite in North Korea about what could happen if they turned their back on the regime.