Mahathir said in a two-line statement that he had informed the country's king of his resignation at 1pm Kuala Lumpur time on Monday, according to Aljazeera.
Mahathir's party, Parti Pribumi Bersatu Malaysia, has also quit the ruling government coalition, Pakatan Harapan (Alliance of Hope), according to the party president, Muhyiddin Yassin, casting doubt on the future of the partnership.
Mahathir's decision follows a weekend of political wrangling, after it was reported on Sunday night that his party was planning to form a new government that would exclude his anointed successor, Anwar Ibrahim.
MNA/PR