"It's a little bit sad to move away," the key defender told Trade Radio.
"I've been there since I was 21 and they were the team that gave me an opportunity.
"The Adelaide Footy Club are rebuilding a little bit now so I saw it as an opportunity to extend my career."
A father to one-year-old daughter Hazel, Hartigan said the opportunity to return to his native state was a chance that was too difficult to ignore.
"It was more the family factor.
"No one has been able to visit us this year (during COVID).
"To come home and have family around was a massive factor, and the opportunity to come to Hawthorn and play in defence."
With James Frawley retiring and James Sicily to miss most of the 2021 season with a knee injury, Hartigan and Sam Frost will represent the Hawks key defensive make-up.
The 28-year-old expressed his excitement about the opportunity of taking on the bigger bodies of opposition forwards and said he is confident of playing well into his 30s.
"I'm not putting any gauges on it being two years - I'd love to play for as long as I can.
"I still feel there's an opportunity to play some really good footy over the next four to five years."