A member of the Democratic Progressive Party, Lin was elected as a Nantou County representative to the Legislative Yuan in 2004. He attempted to aid his father Lin Tsung-nan's 2005 run for the magistracy of Nantou County, stating that, in 2002, competing candidate Tsai Huang-liang had meddled in the affairs of the Taiwan Railways Administration.[2][3] In 2006, he accused Chinese companies of copyright infringement against Taiwanese brands.[4][5] Lin sought to join the Legislative Yuan's Judiciary Committee, but was barred from doing so after the Democratic Progressive Party legislative caucus proposed a ban on committee membership for politicians whose family members were subject to current legal proceedings. This provision targeted Lin and his father, Lin Tsung-nan, who was facing corruption charges at the time.[6] The next year, Lin Yun-sheng supported an amendment to Article 1059 of the Civil Law that permitted people use their maternal surname with the permission of both parents.[7] He ran for reelection in 2008, and lost to Wu Den-yih.[8][9] Lin has received media attention for his connections to convicted criminal Chiang Chin-liang.[10][11]