Former North Korean diplomat Tae Yong-ho has been named the new leader of South Korea's presidential advisory council on unification, APA reports citing BBC.
This makes him the highest-ranking defector among the thousands who have resettled in the South - and the first to be given a vice-ministerial job.
Tae, 62, was Pyongyang's deputy ambassador to the United Kingdom before he fled to South Korea in 2016.
Pyongyang has denounced him as "human scum" and accused him of embezzling state funds and other crimes.
Mr Tae became the first former North Korean to win a seat in South Korea's 2020 National Assembly.
He failed to secure a second term in parliamentary elections in April, but in his new role, he will be be advising South Korean President Yoon Suk Yeol's office on peaceful Korean unification.
"He is the right person to help establish a peaceful unification policy based on liberal democracy and garner support from home and abroad," the presidential office said on Thursday.
Born in Pyongyang in 1962, Mr Tae entered the foreign service at the age of 27 and spent almost 30 years working under three generations of the ruling Kim dynasty.
He said in earlier statements that he left North Korea because he did not want his children to have "miserable lives". He also cited disgust with Kim Jong Un's regime and expressed admiration for South Korea's democracy.
In a memoir published this year, Mr Tae wrote about the excesses of the North Korean elite and the depths of the personality cult built around the Kims.
Since his defection, he has advocated for the use of "soft power" to weaken the Kim regime and called for prisoner swaps between the North and the South.