A midfielder who began his career at Portadown F.C.. Aged 16, and after only 10 league appearances at Shamrock Park he signed for Aston Villa. At Villa, he was part of the 2002 FA Youth Cup winning side, but was unable to break into the first team.
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 Swifts to a 4th place finish in the Carnegie Premier league in the 2005/06 campaign and with that success brought Dungannon Setanta cup football and the season after the clubs 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 Glentoran career.
On February 23, 2009, Scullion joined Derry City FC 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 F.C.
Scored in the Europa League in August 2009.