Thae is one of the highest-level North Korean officials to defect to South Korea.
Defections are a source of bitter contention between the rival Koreas, and South Korea doesn't always make high-profile cases public. North Korea often accuses the South of kidnapping or enticing its citizens to defect, the Associated Press reported.
Wednesday's announcement came as North Korea has responded angrily to a US plan to place an advanced missile defense system in South Korea. The North has warned of unspecified retaliation and fired several missiles into the sea earlier this month.