"I'm sure and I can say that Kim Jong-Un's days are numbered," said Thae Yong-Ho, who fled his post as North Korea's deputy ambassador to Britain in August.
In his first press conference for foreign correspondents, held under tight security, Thae said he was sure that more of his fellow countrymen would follow suit since North Korea was "on a downward path".
The elite were "turning their backs" on leader Kim Jong-Un, he said, adding: "The traditional structures of North Korean systems are crumbling."
Thae is among the highest-ranking defectors from the North for years. He said he had begun to waver as his diplomatic role granted him access to outside information.
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His disillusionment turned to despair after Kim, who inherited power from his late father Kim Jong-Il five years ago, began ruthlessly purging officials, he added.
Kim had his own uncle and one-time political mentor Jang Song-Thaek executed in late 2013 on an array of charges, including treason and corruption.
North Korean diplomats are generally compelled to leave one of their children behind in Pyongyang when they are dispatched abroad, but Thae was able to take both his sons, now aged 19 and 26, to London - easing his preparations to defect.
"The Kim Jong-Un regime abuses love between parents and children to control North Korean diplomats," he said.
After Thae's defection the North's state media denounced him as "human scum" and accused him of embezzling state funds, raping a minor and spying for South Korea in exchange for money.
"The only way to resolve the issue of North's nuclear threats is the elimination of Kim Jong-Un's regime," he said.
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