The defector was a senior colonel with the North Korean Reconnaissance General Bureau, which is in charge of espionage operations against South Korea, according to South Korean Defense Ministry spokesman Moon Sang-gyun and Unification Ministry spokesman Jeong Joon-hee.
North Korea's Reconnaissance General Bureau is a powerful body, responsible for clandestine operations, including espionage against foreign countries and cyberwarfare operations.
On Tuesday, North Korea threatened defectors in a commentary published in its state-run propaganda site Uriminzokkiri, calling them "gangsters little short of thrusting daggers into the lifeline of all families in the DPRK."
Many defectors have expressed concern for their family members who remain in North Korea as the regime is said to practice guilt by association -- in which people closest to the individual are punished.
The North Korean commentary threatened those who defected to South Korea of "pre-emptive, consecutive attack on them in a more deadly and severe punishment without any warning and prior notice."
Fleeing brutality
All North Korean defectors are interviewed by South Korean intelligence services for information about life across the border.
It is expected the latest, high-profile defector could prove a rich trove of knowledge about the workings of North Korean leader Kim Jong Un's secretive regime.
The hard line on aides and officials was eroding Kim's fragile support base, the defector said, in comments CNN was unable to confirm independently because of the challenges of verifying information inside North Korea, one of the world's most closed societies.
Tensions have ratcheted up on the divided Korean Peninsula this year as Pyongyang has made a series of assertions about developments in its military capability.
CNN's Kevin Wang and Madison Park contributed to this report.