The former state poet, who defected to South Korea in 2004, now writes to tell the world about what he calls the brutality of everyday life in the North.
"North Korea has nuclear programs, but South Korea has the media," said Jang, who is in London for a global poetry festival involving poets from countries competing in the July 27 to Aug. 12 London Olympics. "Truth is the strongest weapon."
Jang's poems now tell of public executions, hunger and desperate lives. He said that the piece he chose to submit to London's Poetry Parnassus festival, "I Sell My Daughter for 100 Won," is based on one of his worst memories in North Korea - recollections of a mother trying to sell her daughter in the market place.
"The life of a North Korean is not about living, but about how to sustain life," he said through an interpreter. Jang, dressed in a loose white shirt and cream trousers, spoke quietly but accompanied most sentences with emphatic hand gestures.
Jang Jin-sung is not his real name, according to South Korean news reports.
The U.S. State Department says that North Korea "maintains a record of consistent, severe human rights violations," and the United Nations said in a recent update on the North's humanitarian situation that the food supply remains tenuous for two-thirds of the population.
Pyongyang denies abusing its citizens.
As one of Kim's top state poets, Jang, 40, said he was responsible for glorifying the leader in the poetry he published in the official Workers' Party newspaper. Poets had a special role among Kim's many propaganda artists, Jang said.
"Because of the paper shortage in North Korea, poems were the most efficient, economical way to spread propaganda," he said.
Jang said he led a privileged life in Pyongyang and once dined with Kim, when he found out that the leader was much shorter than he was led to believe because Kim didn't wear his normal high-heeled shoes indoors.
He also recalled being instructed to avoid looking into the leader's eyes and instead to stare at his second shirt button. After more contact with Kim, Jang said he soon stopped believing that he was "this godlike leader of this wonderful country."
Jang said his doubts solidified when, working in the propaganda ministry, he got hold of and read South Korean books. In 2004 he crossed the river to China, where he was wanted by Kim's men, but agents from South Korea found him first. He then worked for the South's intelligence agency for seven years before setting up his own online newspaper about North Korean issues earlier this year.
Jang said he believes the current regime in the North is bound to break down - not least because of the instability brought about by Kim's death in December.
He said the son and young successor, Kim Jong Un, lacks the power and experience of his father and is surrounded by his father's men. He did not elaborate on what serves as the basis for his beliefs on the current political situation in the North.
"It's all about rivalries between the generations," he said. "They don't have the experience to deal with a situation like this, with so much power struggle. For Kim Jong Un to sustain himself he's got to have a strong rule, controlling his people through fear of punishment or fear of reprisal."
Jang is appearing at the Parnassus festival—a gathering of poets that organizers claim is the largest poetry festival ever staged in the United Kingdom.
Other participants included Afghanistan's Reza Mohammadi, Kay Ryan from the United States and Karlo Mila from New Zealand.
Sylvia Hui can be reached at twitter.com/sylviahui
Jang's poetry, translated into English, can be read at