The government's first public endorsement of the younger Kim as successor came during a memorial memorial service for his father in the capital, Pyongyang, a day after his funeral was held.
More from GlobalPost: Kim Jong Il's funeral procession decoded
Kim Jong Il, who ruled North Korea since the death of his father Kim Il Sung in 1994, died of a heart attack on December 17.
During today's service – broadcast live on state television from the city's main Kim Il Sung Square – Kim Jong Un stood on the balcony of the Grand People's Study House, surrounded by top government and army officials looking down on a million-strong crowd, the AP reported.
North Korea's number two leader, Kim Yong Nam, told the crowd of a million North Koreans assembled below that their grief would be turned into strength "1,000 times greater under the leadership of comrade Kim Jong Un," the BBC reported.
Kim Yong Nam said:
"Respected Comrade Kim Jong Un is our party, military and country's supreme leader who inherits great comrade Kim Jong Il's ideology, leadership, character, virtues, grit and courage. The fact that he completely resolved the succession matter is Great Comrade Kim Jong Il's most noble achievement."
Kim Jong Gak, a top military official, told the crowd the military would also serve Kim Jong Un “at the head of our revolutionary troops,” the BBC reported.
Those surrounding Kim Jong Un, who is in his late 20s and has little political experience, included Kim Jong Il's younger sister, Kim Kyong Hui, and her husband Jang Song Thaek, who the AP said would likely act as mentors to the new leader.
Kim Jong Il's two older sons, Kim Jong Nam and Kim Jong Chol, were not seen at the funeral, the BBC reported.
Meanwhile, a defector from North Korea who formerly worked for the regime said in an interview this week that Kim Jong Un will push for a more open North Korea, according to Bloomberg News. He is the latest in a string of North Korea observers to make this prediction.
“It’s better for North Korea to have Kim Jong Un as their leader than anyone else,” said Choi Se Woong, former deputy governor of the North’s Korea Reunification Development Bank and the son of a former North Korean finance minister. “Kim Jong Un will seek to start a market economy but it will be uniquely North Korean-style, different from China, South Korea or any other capitalist country.”
More on GlobalPost: Will North Korea change for the better?