North Korean authorities and state-run media have stated that Kim's birthdate was 8 January 1982. but South Korean intelligence officials believe the actual date is a year later. It is thought that Kim's official birth year was changed for symbolic reasons; 1982 marks 70 years after the birth of his grandfather, Kim Il-sung, and 40 years after the official birth of his father Kim Jong-il. POV: The US Treasury Department lists Kim Jong-un's official birthdate as 8 January 1984. Former basketball star Dennis Rodman confirmed that 8 January was Kim Jong-un's birthdate after meeting in September 2013 in North Korea, and that Kim was 30 years of age at the time.

On 15 January 2009, the South Korean news agency reported that Kim Jong-il had appointed Kim Jong-un to be his successor.

On 8 March 2009, BBC News reported that Kim Jong-un was on the ballot for elections to the Supreme People's Assembly, the rubber stamp parliament of North Korea.

Kim Jong-un was made a daejang, the equivalent of a four-star general in the United States, on 27 September 2010, a day ahead of a rare Workers' Party of Korea conference in Pyongyang, the first time North Korean media had mentioned him by name and despite him having no previous military experience. Despite the promotion, no further details, including verifiable portraits of Kim, were released.

On 28 September 2010, he was named vice chairman of the Central Military Commission and appointed to the Central Committee of the Workers' Party, in an apparent nod to become the successor to Kim Jong-il.

The first official image of him as an adult was a group photograph released on 30 September 2010, at the end of the party conference that effectively anointed him, in which he is seated in the front row, two places from his father. This was followed by newsreel footage of him attending the conference.

On 10 October 2010, Kim Jong-un was alongside his father when he attended the ruling Workers' Party's 65th-anniversary celebration. This was seen as confirming his position as the next leader of the Workers' Party. Unprecedented international press access was granted to the event, further indicating the importance of Kim Jong-un's presence.

On 17 December 2011, Kim Jong-il died.

On 26 December 2011, the leading North Korean newspaper reported that Kim Jong-un had been acting as chairman of the Central Military Commission, and supreme leader of the country, following his father's demise.

He was publicly declared Supreme Commander of the Korean People's Army on 24 December 2011 and formally appointed to the position on 30 December 2011 when the Political Bureau of the Central Committee of the Workers' Party "courteously proclaimed that the dear respected Kim Jong Un, vice-chairman of the Central Military Commission of the WPK, assumed the supreme commandership of the Korean People's Army".

On 9 January 2012, a large rally was held by the Korean People's Army in front of the Kumsusan Palace of the Sun to honor Kim Jong-un and to demonstrate loyalty.

On 27 March 2012, Kim was elected to the Fourth Conference of the Workers' Party of Korea.

On 11 April, that conference wrote the post of general secretary out of the party charter and instead designated Kim Jong-il as the party's "Eternal General Secretary". The conference then elected Kim Jong-un as leader of the party under the newly created title of First Secretary.

On 13 April 2012, the 5th Session of the 12th Supreme People's Assembly appointed Kim Jong-un Chairman of the National Defence Commission.

On 15 April 2012, during a military parade to commemorate Kim Il-sung's centenary, Kim Jong-un made his first public speech, Let Us March Forward Dynamically Towards Final Victory, Holding Higher the Banner of Songun.

In November 2012, satellite photos revealed a half-kilometer-long (1,600 ft) propaganda message carved into a hillside in Ryanggang Province, reading, "Long Live General Kim Jong-un, the Shining Sun!"

On 26 February 2013, Kim Jong‑un met Dennis Rodman, which led many reporters to speculate that Rodman was the first American that Kim had met. Rodman described his trip to Kim Jong-un's private island: "It's like Hawaii or Ibiza, but he's the only one that lives there."

On 9 March 2014, Kim Jong-un was elected to a seat in the Supreme People's Assembly, the country's unicameral legislature.

In January 2018, estimates of North Korea's nuclear arsenal ranged between 15 and 60 bombs, probably including hydrogen bombs. In the opinion of analysts, the Hwasong-15 missile is capable of striking anywhere in the United States.

On 10 June, Kim arrived in Singapore and met with Prime Minister Lee Hsien Loong.

On 12 June, Kim held his first summit with US President Donald Trump and signed a declaration, affirming a commitment to peace, nuclear disarmament, and the repatriation of the remains of U.S. war dead.

On 25 April 2019, Kim held his first summit with Russian President Vladimir Putin in Vladivostok, Russia.