After two years at West Adelaide, Walsh made it on Melbourne's rookie list and was runner-up in the 1998 Gardiner Medal with good performances in the reserves.
The following season he missed just one game and had 20 disposals from a half back flank in the 2000 AFL Grand Final loss to Essendon.
His best football was played in 2001 and he polled 11 votes at the Brownlow Medal to finish as the top placed Melbourne player, with three best on grounds.
Melbourne traded him to Port Adelaide in the 2004 AFL draft, gaining pick 43 as a result, which they used to recruit Michael Newton.
He struggled with injury in 2006 and at the end of the season was delisted by Port Adelaide who were pushing for youth.