Stocker was cut from the Blues at the end of last season after four years and 28 games at senior level, having joined Carlton as a first-round pick in the 2018 National Draft.
With two list spots vacant, the Saints confirmed on Friday that Stocker was signed to a rookie position ahead of the new campaign.
“I couldn't be happier to sign on as a Saint,” Stocker said in a club statement.
“The last few months have reaffirmed to me how much I want this and I really believe I can contribute at AFL level. I'm very thankful to my coaches and those around me for giving me this chance.
“As a lifelong Saints fan, I'm looking forward to seeing what the club's 150th year will hold and I'm stoked to be a part of it.”
The Saints, who have welcomed the return of senior coach Ross Lyon ahead of the 2023 season, will look to utilise Stocker's disposal and run to add another edge to their midfield pack.
“We're pleased to offer Liam a place on our list for the upcoming season,” Executive General Manager of Football Geoff Walsh said.
“Liam has been holding nothing back over the past few months and has really proven to us that he's got the right qualities and mindset we believe will make an impact within our side.
“His contested work is one of his key strengths, as is his ability to use both feet, and we look forward to seeing him make the most of his opportunity with St Kilda.”
St Kilda will have until February 15 to decide on signing another SSP talent, or can opt to hold a list spot open for the Mid-Season Draft.