Hwang had been seen as the best hope of challenging the domination of liberal frontrunner Moon Jae-in based on popularity surveys, as conservative politics has taken a beating over its association with scandal-hit former President Park Geun-hye.
“To stabilize state affairs and fairly administer the presidential election, I’ve reached the judgment that it is inappropriate for me to run in the election,” Hwang was quoted as saying at a Cabinet meeting by Yonhap News Agency.
Hwang was picked as Park’s prime minister before taking over as interim president following her parliamentary impeachment in December.
May 9 had already been touted as the most likely election date because of a 60-day legal countdown set in motion by last Friday’s Constitutional Court decision to uphold Park’s impeachment.
With the date confirmed, it has been marked as a public holiday in a nation that was expected to go to the polls in December.
The floor leaders of three out of four major South Korean parties also agreed Wednesday to push for a referendum on constitutional reform on the same day as the election.
But as the main opposition Democratic Party is against the move, it is uncertain whether the required two-thirds of parliament would back the motion.
One of the key questions being debated is whether to swap the country’s single five-year presidential term limit for two four-year terms.