Armitage was drafted by the Saints with pick Number 9 in the 2006 AFL Draft. He grew up in the rugby league stronghold of Mackay in central Queensland, played for Morningside in an AFLQ grand final as a 17-year old.
At the NAB National Draft Camp he impressed with finishing first in the "Agility Test and placed in the top 10 for both the "Beep Test" and 3 km Time Trial.
Armitage made his AFL debut in Round 8, 2007 against Hawthorn.
Armitage played in St Kilda’s 2008 NAB Cup winning side - the club's third preseason cup win.
Armitage played in three of 22 matches in the 2009 season's home and away rounds in which St Kilda qualified in first position for the finals series, winning the club’s third minor premiership.
As of the end of the 2009 season, Armitage had played in two finals series matches and one preseason cup final.