Oh was reelected to his second term in 2010 but resigned in 2011, partly due to the rejection of his proposal under the Seoul free lunch referendum.

[6] In 2012, Oh spent time in London, United Kingdom as a fellow in the Faculty of Social Science & Public Policy at King's College London, focusing on major cities around the world and seeking ways to create jobs and help promote economic growth.

[7] In the 2020 parliamentary election at the Gwang-jin district, he lost to Ko Min-jung, a political newcomer.

He later won the election, defeating Democratic Party nominee Park Young-sun with 57.5 percent of the votes.

[10] This was his first official trip representing Seoul on the sidelines of the United Nations General Assembly meeting.

From 2006 to 2011, Oh announced that he would make Seoul a city of water,[13] and carried out the Han River Renaissance project to build riverside bike paths and Sebitseom floating islands on the southern bank of the Han by Banpo Bridge.

In March 2023, during an interview with Reuters, he said that "we've come to a point where it is difficult to convince people with the logic that we should refrain from developing nuclear weapons and stick to the cause of denuclearisation".