The 32-year-old, known as 'The Package', kicked 48 goals for the Giants in 2026 but was let go at the end of the season as the club turned its eye to the future.
Stringer joins a Saints outfit that missed the finals for a third consecutive season under Ross Lyon in 2026, finishing 11th as injury-riddled spearhead Max King managed just one game.
Lyon will have a new-look forward-line at his disposal next year, with Stringer arriving after ruck-forward Rowan Marshall moved to Geelong.
"Jake has a proven ability to hit the scoreboard and we believe he can add another dimension to our forward line," Saints football manager Lenny Hayes said
"Jake's experience and goal kicking ability will complement the talent we already have while giving us greater flexibility and depth in attack."
Originally from Bendigo, Stringer was drafted by the Western Bulldogs in 2012 and featured in the drought-breaking 2016 premiership under Luke Beveridge.
He spent five seasons at the Bulldogs and seven at Essendon before playing the last two years with GWS.
Stringer confirmed his Giants exit in August ahead of his 250th AFL game, but was adamant he could keep delivering at the top level.
"I definitely feel like I've got quite a few more years left," he said at the time.
Stringer has kicked 440 career goals, with last season's tally of 48 his second-best over his 14 AFL years.
It included a career-high seven goals in a match-winning display against eventual runners-up Fremantle, as well as a haul of six against Adelaide and two bags of five.
St Kilda and Stringer have agreed contractual terms, with their deal to be formalised when the delisted free agency period opens on November 2.
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