Harmison is the younger brother of England paceman Stephen Harmison and played for Northumberland up to Under-15 level before joining Durham.
He was called up into the England squad for the Under-19 World Cup in Bangladesh in 2004 when fellow Durham academy player Mark Turner was ruled out with an ankle injury.
Harmison was then selected for the Under-19 tour of India in 2005 and took 4-58 in the second Test - the best bowling figures by an England bowler during the tour.
He also shone with the bat, making 65 in the third Test, but could not prevent a 3-0 series defeat, before featuring in three of the five one-day internationals.
Harmison signed a professional contract with Durham in October 2005 and, unlike his brother, played as a specialist batsman in a solid 2006 season.
2007 saw him play for the first-team more regularly, scoring 251 runs in eight LV County Championship innings, including his maiden first-class century.
Although he struggled for consistency in 2008, he played in 12 of Durham’s championship matches during their inaugural title-winning season.
In 2009 he made no Championship appearances, however he did manage to keep up his one-day appearances - the highlight of which was 67 in the NatWest Pro40.