[6] He started his political career in 1988 as assistant administrator in the Office of Planning & Coordination of the Peace Democratic Party.

[2][7] Then, he became closer to the party chairman, Kim Dae-jung (aka DJ), who was later elected the President of the Republic.

[2][7] After the election of Moon Jae-in in 2017, Yun was considered a potential candidate for the newly-created Minister of SMEs and Startups[9][10] but was not appointed.

[11] On 16 April 2021, Yun was elected the new parliamentary leader of the Democratic Party, defeating Park Wan-joo.

[2] On 27 March 2021, during the campaign of Park Young-sun, who was running for Mayor of Seoul in the 2021 by-elections, Yun told people, "There is a candidate who keeps lying, even though he knows he owns a property in Naegok-dong.

"[18] The PPP subsequently condemned his remarks as "severe hate speech" and "ruinous social splitting that must be stopped immediately.