Kim made the promise to Chinese president Xi Jinping during his third trip to Beijing since March, a visit which observers see as further helping to rebuild historic ties between the two former Cold War allies.
The North Korean leader told Mr Xi he would work with China on "opening a new future" on the Korean peninsula, according to the official Korean Central News Agency (KCNA).
The leaders discussed denuclearisation, KCNA said, while Kim was also thought to have briefed Mr Xi on his historic summit with Donald Trump last week.
The meeting in Singapore - the first between sitting leaders of the United States and North Korea - included commitments by Kim to work toward denuclearisation in exchange for US security guarantees.
For his part, Mr Xi was reported to have offered to help turn the summit deal into a reality.
Kim was quoted in Chinese media saying he "felt thanks for and highly praised China's promotion of denuclearisation of the Korean Peninsula and its important role in protecting the peninsula's peace and stability."
The young leader has been seeking to reassure Beijing that he will not forsake China's interests as he negotiates with the US.
And he was being treated to all the trappings of a traditional state visit in the Chinese capital during his two-day visit, which ends on Wednesday.
He was greeted by waving school children and a military honour guard at the ornate Great Hall of the People on Tuesday.
Kim's first visit to China - and his first foreign trip as leader - came in March, when he arrived in Beijing in an armoured train from Pyongyang. He also met Mr Xi in the northern port city of Dalian in May.
Both previous visits were not announced by China's tightly-controlled media until Kim had left China, but this week's trip has been heavily covered in newspapers and on television bulletins.
China is North Korea's only diplomatic backer and key trading partner. However, relations deteriorated as Pyongyang carried a series of missile tests last year and China backed hard-hitting sanctions.