Gilham's junior career was distinguished, playing for Oakleigh Chargers in the TAC Cup and in 2002 he was chosen to captain the Victoria Metro under 18 side in the national carnival. A skinny defender, Gilham was taken by Port Adelaide with its first pick (pick 16 overall) in the 2002 AFL Draft.
Port Adelaide
Gilham's three seasons at Port Adelaide were hampered by groin and shoulder injuries, together with difficulty gaining the strength to succeed as a key defender in the AFL. Gilham only managed one senior game during his time in South Australia, in 2005 as result of an injury and illness to two other players. He was delisted at the end of the season.
Gilham's return to Victoria (and the AFL) came courtesy of Hawthorn, who selected him with pick 34 in the 2006 Rookie Draft.