After graduation, Moon entered the Kyung Hee University, where he majored in law. He was arrested and expelled from the university when he organized a student protest against the Yushin Constitution. Moon Jae-in was sentenced to eight months in prison with a suspended sentence of one year, and then drafted into the Marine Corps. During his military service, he entered into the special forces, where he participated in various missions, including the response operation following the so-called 1976 Axe Murder Incident, in which North Korean soldiers killed two US Army officers in the Korean Demilitarized Zone.
In 1980, he passed the state examination for the right to practice law. Moon had planned at becoming a judge, but because of his participation in protests during his university years, he was turned down for the position. Deciding to become a lawyer instead, he went to Busan, where he met with the future president of South Korea, Roh Moo-hyun.
Between 2007 and 2008, Moon was the head of Roh's presidential staff.
Since 2009, Moon Jae-in was the executive director and from 2010 the chairman of the Roh Moo-hyun foundation.
In 2012, Moon participated in the presidential elections, and received 48 percent of the vote, but ultimately lost to Park Geun-hye.
Between 2012 and 2016, he was a member of the Korean National Assembly and from 2015 to 2016 was the chairman of the Democratic Party of Korea.
In April 2017, Moon was registered as a candidate for the presidency of the Republic of Korea. On May 9, Moon achieved a sweeping victory in the snap presidential elections, defeating his two rivals: conservative Hong Joon-pyo, who received 24.03 percent of the vote, and centrist Ahn Cheol-soo, who received 21.41 percent of the vote.
On Wednesday, Moon in accordance with the National Election Commission's decision, officially assumed the post of President of South Korea.