The announcement by Regmi came during his live address to the nation today.
Regmi, in his address to the nation, said that he was happy to hand over the mantle to the newly elected government led by Koirala.
He expressed hope that the new administration under Koirala would be successful in drafting the constitution within a year, which would be his biggest reward.
During his address, Regmi also lauded his council of ministers and government bodies for successfully carrying out the responsibility of the Constituent Assembly election at a difficult time.
Regmi had assumed office as the head of government in mid-March last year with the task of holding the election to the Constituent Assembly as per the request of the major political parties.