North Korea has replaced its second most powerful military official with Ri Yong Gil.
Pak Jong Chon was previously the vice chairman of the Central Military Commission.
No reason was given for the change, which occurred at the party's annual meeting.
Pak had a key role in developing the country's short-range missile technology.
In late 2020, he was promoted to the politburo and given the title of marshal.
Ri, Pak's successor, has held key military positions, including the defence minister.
The change in leadership comes amid increased tension with South Korea.
Some experts believe Pak may have been responsible for security failures related to North Korean drones.