Walsh, 22, who spent last year on St Kilda's rookie list, will play his first game in Saints colours after moving from Ireland 15 months ago.
Saints coach Ross Lyon said on Tuesday he would look to use Walsh in several roles, including as support for ruckman Ben McEvoy.
"(He will play at) full-back and forward. He is a key position player. He might not like hearing he's going into the ruck but it's an opportunity for him," Lyon said.
"He came fourth or fifth in the Sandringham best and fairest (in 2010). It's a pretty high standard and to deliver on that has exceeded everyone's expectation."
The Saints ruck stocks are a little bare with Michael Gardiner and Justin Koschitzke both out through injury, while Rhys Stanley will miss the entire NAB Cup after a club-imposed suspension for breaking team rules on a recent trip to New Zealand.
"Rhys has passed up a wonderful opportunity with Gardiner and Koschitzke being out through injury," Lyon said.
"That creates an opportunity for (Daniel) Archer and Jason Blake can ruck a bit as well. It creates an opportunity for others."
Nick Winmar also looks set to debut for the Saints after battling through injury in his first year with the club.
The second cousin of St Kilda great Nicky Winmar was drafted by the Saints in 2009 as a running half-back.
Lyon said he was one of several young Saints who would get an opportunity throughout the pre-season to show their worth.
He named Tom Lynch, Alistair Smith and Winmar as likely selections.
"There is a bit to unveil - Archer and Walsh as well. It's a combination of exposing those players and building to round one," he said.
"We won't have played a practice game and it will be our first hit out. We are not expecting miracles but our motto is anywhere, any time, any opposition."
But some of the Saints stars will have to wait to kick off their seasons.
Captain Nick Riewoldt will not play against the Lions and the Bombers, while Koschitzke, Gardiner and Sam Gilbert will also miss.
"They are a bit behind. Sammy Gilbert had some tightness of the hamstring last week so he is a week behind where we need him to be. He is critical for us."
