David returned home and joined home town club Glenavon, before moving to Dungannon Swifts in 2003.
Under Joe McAree, Scullion was a key member of the Dungannon Swifts team and played a huge role in guiding the club to a 4th-place finish in the Carling Premier league (Now the Danske BankNIFL Premiership) in the 2005/06 campaign and with that success brought Dungannon SwiftsSetanta cup football and the season after the club's first ever European outing against Icelandic Opposition.
David was also a key member of Roy Millar's Northern Ireland Under 21 squad for the 2005/06 season and retained his place for the European qualifiers at the start of the new domestic season. Scullion is an attacking midfielder and finished his last season with the Swifts with 13 goals.
He joined Glentoran on 16 June 2007 for a fee believed to be around the £10,000 mark and scored 15 goals in 64 appearances in his time with the club.
On 23 February 2009 Scullion joined Derry City in a one-year deal on the last day of the League of Ireland transfer window.
In July 2010, David signed a 1-year deal with Irish Premier League side Coleraine
On 1 July 2013 Scullion rejoined Glentoran F.C. on a three-year contract. In February 2015, he signed a two-year contract extension. On 2 May 2015, Scullion scored the winning goal in the 2014-15 Irish Cup final to grant Glentoran their 22nd Cup win. In May 2016, he was transfer listed as a part of Alan Kernaghan restructuring of the squad.
He joined Larne F.C. in the autumn of 2017 and helped the club win the Championship title in 2018/19.
