A tax lawyer in 1981, Roh defended one of two dozen students who had been arrested and tortured for nearly two months for possessing banned literature. As a result of the experience, Roh stated his "comfortable life as a lawyer came to an end." Roh dedicated the rest of his law career to defending those who suffered abuse of their human rights, as well as defending labor organizers. He became involved in the pro-democracy movement in 1987 against the leadership of Chun Doo Hwan, for which he was briefly jailed. In September 1987 he was again imprisoned, this time on charges of supporting striking workers.
Roh entered politics the following year, winning a parliamentary seat from Pusan in 1988. He gained a name for himself by interrogating army leaders over a 1980 massacre of protesters, and for interrogating top officials from the Chun administration about allegations of corruption. He lost his seat in the National Assembly in 1992 and his bid for the mayorship of Pusan in 1995 was also unsuccessful. He returned to Parliament in 1998. He lost the 2000 election for his parliamentary seat but his supporters created a fan club called Nosamo (Roh lovers' group). The group's website was influential in his rise within the Millennium Democratic Party (MDP) and then in the following year. He was elected a member of the MDP's Supreme Council in 2000. His most prominent government position before becoming president was as Minister of Maritime Affairs and Fisheries from August 2000 to March 2001.
Roh's chances of winning the MDP nomination for president were seen as slim before the primaries began in March 2002. He secured 72.2% of the ruling party's votes in the primaries, however, defeating Chung Dong Young, a former television anchor who took 27.8% of the votes. Roh's support came from younger voters, especially college-educated members of the "baby-boom" generation with liberal political views and experience with the pro-democracy movements of the 1980s and early 1990s. He also gained support from the poor and underprivileged. In the 19 December 2002 presidential election Roh took 49% of the popular vote to Lee Hoi Chang's 46.5%, with Lee representing the Grand National Party. Roh was inaugurated president on 25 February 2003.