A rare meeting of the ruling party in North Korea has opened the way for Kim Jong-il to hand power to his youngest son.
The Workers Party, which had not met for 30 years, convened hours after Kim Jong-un was made a four-star general, even though he has no military experience.
State media report his father, who is thought to be in poor health, was re-elected as leader.
Kim Jong-un is now a member of the Central Committee of the ruling Workers Party and is part of the National Defence Commission.
Until Tuesday, there had been no mention of Kim Jong-un by state media.
He had already been identified as the most likely successor to the Communist dynasty started by his grandfather, Kim Il-sung, in 1948.
Little is known of him other than that he was educated in Switzerland and is about 27 years old.
The BBC reports his elder brother and half-brother appear to have been ruled out of the running for the succession.
Kim Jong-il is said to have had a stroke two years ago, and was given treatment in China.