“From 21 April, North Korea will stop nuclear tests and launches of intercontinental ballistic missiles,” the Korean Central News Agency said.
The decision is aimed at pursuing economic growth and peace on the Korean peninsular, state media report.
Mr Kim is due to meet his South Korean counterpart Moon Jae-in next week.
He is also expected to hold an unprecedented summit with US President Donald Trump by June. If it takes place, it will be the first meeting between a sitting US president and a North Korean leader.
Later on Saturday, Trump welcomed Kim’s move.
“This is very good news for North Korea and the World – big progress!,” Mr Trump tweeted after Kim Jong-un’s announcement.
On Thursday, the US leader said there was a “bright path available to North Korea when it achieves denuclearisation”.
“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 President Moon Jae-in’s office said.
The official Korean Central News Agency (KCNA) said that Pyongyang would also close its nuclear test site as part of the country’s efforts to pursue economic growth and regional peace.
“Nuclear development has proceeded scientifically and in due order and the development of the delivery strike means also proceeded scientifically and verified the completion of nuclear weapons,” the agency quoted Kim as saying during a meeting of the ruling party’s full Central Committee.
“We no longer need any nuclear test or test launches of intermediate and intercontinental range ballistic missiles, and because of this the northern nuclear test site has finished its mission.”
According to the KCNA statement, North Korea also pledged to join international efforts to stop all nuclear tests and vowed to never use nuclear weapons as long as there are no such threats towards the country.
“The North appears to be signalling now, through its state news agency, that it is shifting its focus from the nuclear weapons development to more of an economic policy,” Al Jazeera’s Kathy Novak, reporting from South Korea’s capital, Seoul, said.
Last year, after conducting its most powerful nuclear test ever and saying it had successfully tested its first intercontinental ballistic missile, North Korea announced that its nuclear programme was complete, added Novak.
Next week’s inter-Korean summit will the the first such meeting since 2007 and only the third since the 1950-1953 Korean War.
Meanwhile, Kim’s expected meeting with Trump will come after months of a diplomatic standoff that saw the two leaders exchange fiery military threats and personal insults.
A date for the meeting has not yet been set, with the White House still weighing five potential locations, according to comments made by Trump to reporters on Tuesday.