Sherlock first became directly involved in politics when he served a six-month internship with MEPProinsias De Rossa, in his office at the European Parliament. Following the completion of his internship he was offered a full-time job working as an assistant to de Rossa. In 2002, Sherlock served as election manager for his father in his attempt to win back a seat in the Cork East constituency at the general election as a Labour Party candidate. The campaign was successful; Joe Sherlock returned to Dáil Éireann after a ten-year absence. The abolition of the dual mandate in 2003 meant that Joe Sherlock had to vacate his seats on MallowTown Council and Cork County Council. Seán was chosen as his replacement and he was co-opted onto both councils that year. The following year he won both seats in his own right when he was successful at the local elections. He was then elected Mayor of Mallow. When Joe Sherlock announced that he would not be contesting the 2007 general election, Seán was once again chosen as a replacement candidate. He contested Cork East for the Labour Party and was elected. A Fianna Fáil-headed government returned to power once again. Seán Sherlock was subsequently appointed Labour Party Spokesperson on Agriculture and Food. Sherlock retained his Dáil seat at the 2011 general election, topping the poll in Cork East. When the new coalition government was formed he was tipped for possible inclusion in the cabinet; however, he joined the junior ministerial ranks as Minister of State for Research and Innovation.
Copyright legislation
In January 2012, Sherlock proposed legislation to give copyright holders the right to seek an injunction against copyright violators. A group called 'Stop SOPA Ireland' petitioned against the legislation, comparisons being made between these reforms and the Stop Online Piracy Act in the United States. Sherlock said such comparisons were "not based on fact". According to the Irish government the legislation was intended to close a loophole after a High Court case in 2010, in which EMI sued UPC, an internet service provider, over illegal downloads. A denial-of-service attack was performed against government websites in protest over the changes. On 29 February 2012, Sherlock signed the legislation into law. He cited Ireland's "obligations under EU law". The legislation subsequently resulted in the blocking of The Pirate Bay in Ireland.