“From 21 April, North Korea will stop nuclear tests and launches of intercontinental ballistic missiles,” the country’s state news agency said.
Mr Kim said further tests were unnecessary because Pyongyang’s nuclear capabilities had been “verified”.
The surprise announcement comes as North Korea prepares for historic talks with South Korea and the US.
Mr Kim is due to meet his South Korean counterpart Moon Jae-in next week for the first inter-Korean summit in over a decade, and US President Donald Trump by June.
Both countries have been pushing Pyongyang to denuclearise and they reacted positively to the latest development.
“This is very good news for North Korea and the World – big progress!” Mr Trump tweeted after the announcement.
On Thursday, the US leader said there was a “bright path available to North Korea when it achieves denuclearisation”.
A spokesperson for the South Korean president called the North’s move “meaningful progress”.
“It will also contribute to creating a very positive environment for the success of the upcoming South-North summit and North-United States summit,” a statement from Mr Moon’s office said.
The decision to suspend missile launches was made during a meeting of the ruling party’s central committee on Friday, the Korean Central News Agency (KCNA) said.
In a statement quoted by the agency, Mr Kim said it was no longer necessary to conduct missile tests because “nuclear weaponisation” had been achieved.
“The northern nuclear test site has completed its mission,” he said.
This echoes a previous statement made during a New Year address in which Mr Kim declared his nuclear and ballistic missile programs completed.
After six nuclear tests North Korea may feel it does not need to upgrade its existing designs, says the BBC’s Laura Bicker in Seoul.
Although Pyongyang said it would abolish its nuclear test site, there is no indication it is planning to get rid of its existing weapons.
The decision to halt missile tests is also aimed at pursuing economic growth, according to KCNA. Mr Kim reportedly pledged to “concentrate all efforts” on developing a socialist economy during Friday’s meeting. (Courtesy BBC)