The meeting decided to dismiss Jang from all his posts and expel him from the Workers' Party, KCNA said. Kim Jong Un attended and "guided" the meeting, it said.
KCNA listed a series of acts committed by Jang that it said led to the decision to remove him, including mismanagement of the country's financial system, corruption, womanizing and abusing alcohol and drugs.
"Jang pretended to uphold the party and leader but was engrossed in such factional acts (such) as dreaming different dreams and involving himself in double-dealing behind the scene," KCNA said.
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"Affected by the capitalist way of living, Jang committed irregularities and corruption and led a dissolute and depraved life."
Jang is married to Kim's aunt, the daughter of the North's founding leader Kim Il Sung, and was widely considered to be working to ensure his nephew firmly established his grip on power in the past two years.
Last week a South Korean official said Jang was likely alive and in no immediate physical danger, as was his wife, Kim Kyong Hui.
Experts say Jang's removal will help the younger Kim consolidate his power base with a group of younger aides.
Jang had been a prominent fixture in many of the reports and photographs of Kim Jong Un's public activities, but his appearances have tapered off sharply this year and he has not been since in official media since early November.
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South Korean media said on Friday that a man who managed funds for Jang had fled and sought asylum in South Korea.
The aide, who has not been not named, was being protected by South Korean officials in a secret location in China, cable news network YTN and the Kyunghyang Shinmun newspaper said, citing sources familiar with the matter.