Hong made the announcement at the team's training camp in Guadalajara after results on Saturday meant South Korea would not advance to the last 32 as one of the eight third-placed finishers in the group phase.
"I would like to sincerely apologise to the citizens who have loved Korean football and always supported the national team," Hong said.
"Today, I wish to step down as head coach of the South Korean national football team. Accepting this role was never an easy decision for me.
"However, once I made that decision, I did not consider any other reasons. I believed my only task was to fulfil the responsibility entrusted to me to the end."
Hong was appointed in July 2024 as the long-term replacement for Jurgen Klinsmann and steered the country to an 11th successive World Cup appearance.
Expectations were high that a Korean squad featuring Son Heung-min, Lee Kang-in and Kim Min-jae would advance to the knockout rounds from a group featuring co-hosts Mexico, the Czech Republic and South Africa.
The Koreans started with a 2-1 win over the Czechs but losses to Mexico and South Africa left them needing results in other groups to go their way to progress to the next phase of the competition.
"I failed to deliver the results the public expected," said Hong. "The responsibility lies entirely with me."
FIFA World Cup 2026
The 2026 World Cup is taking place from June 11th to July 19th in the United States, Canada and Mexico. The tournament features 48 national teams and is played at 16 modern stadiums.
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