The sacking of Mr Jang for mismanaging the economy, corruption, womanising and drug-taking comes after South Korean reports that one of his aides has sought asylum in South Korea.
Mr Jang was removed from all his posts and expelled from the ruling Workers' Party during a meeting of its politburo on Sunday, the North's official KCNA news agency said. Kim Jong Un attended and "guided" the meeting, it said.
North Korean state television showed a still photograph of Mr Jang being hauled away by uniformed guards from a large conference hall as it reported on the politburo meeting.
Mr Kim's uncle has also been digitally edited out of pictures and video footage and experts said his name was no longer searchable on the KCNA database.
The decision to remove Mr Jang was widely reported in North Korea's media in contrast to the dismissal of officials in the past which were almost never reported.