Hawthorn National Recruiting and List Manager Mark McKenzie paid tribute to the 30-year-old for his services during his brief stint at Waverley Park.
“Kyle has been a great leader and competitor during his time at the club, and has had a strong influence on our group both on and off the field,” McKenzie said.
“We thank Kyle for his service, and we wish him and his family all the best in his future endeavours.”
St Kilda have been linked with a move for Hartigan throughout the week, keen to add to their key defensive stocks this off-season.
RSN's Mark Stevens reported that the Saints have an interest in Hartigan, with a potential two-year deal on offer for the rookie draft selection.
"They're looking to beef up their key defensive stocks.
"He's a free agent so I'd say he'd be at another club next year. If that's the case [he] could be down at Moorabbin.
"I think he's run his race at Hawthorn. (Sam) Mitchell has had plenty of chances to play him. So watch this space there."
Having been spared in the first round of list culls made by the Hawks that included Tom Phillips, Daniel Howe, Jackson Callow and Connor Downie, Hartigan's departure comes only a day after the link between he and the Saints emerged.
Recycled players aren't a foreign concept to St Kilda with their list currently holding 11 players who were originally drafted by other clubs. That number is reduced from what they carried through this past season with the retirements of Paddy Ryder, Dean Kent and Dan Hannebery.
Hartigan is now available for the Saints as a delisted free agent should they opt to bring him to Moorabbin.