Mark Farren began his football career with a largely unsuccessful period, throughout which he was dogged by injury, in the youth setup at Tranmere Rovers. Following this and a spell at Huddersfield Town, he returned to his home county to play for Finn Harps. After only one substitute League appearance in the 2000–01 League of Ireland season and a lack of first-team opportunities saw Farren move south to fellow League of Ireland First Division side Monaghan United. He became a regular in the Monaghan team and quickly gained a reputation as a promising, pacy striker with lots of potential. He earned a move to Derry City in 2003 with a free transfer. Mark Farren stayed clear of injury in the 2005 season to produce some magnificent displays. He finished the season as second top scorer with 18 league goals in 31 appearances and 22 goals in all competitions. It was this excellent form that saw him named PFAI Player of the Year. With the signing of Kevin McHugh and the establishment of Gary Beckett as a top forward in League of Ireland football, Farren’s starting place was placed under threat for the 2006 season. However, he returned to the form he showed in 2005 and did manage to hold down a regular spot in the team, with an especially strong finish to the season, which helped Derry win the FAI Cup. His efforts also helped keep Derry in the league title race up until the very last day of the season, only to see his club lose the title to Dublin rivals, Shelbourne, on goal difference. In all, Farren finished the 2006 season with 18 goals to his name.

In 2010 Mark Farren was instrumental in Derry gaining promotion from the First Division scoring 20 goals in the season. Farren who scored in the 1–0 victory in the last game over Monagahan United to give Derry the championship may however be forced to put his playing career on hold due to a brain tumour. In August 2012 it was announced that he would be moving to Glenavon in January 2013 after signing a pre-contract agreement. In September 2012 he overtook Liam Coyle as Derry’s top scorer with 113 goals. He made his IFA Premiership debut for Glenavon on 5 January 2013 and scored his first goal at Dungannon Swifts. Mark Farren died of cancer on 3 February 2016.