Hartlett was delisted by the Power at the conclusion of this season, ending a 13-year career with the club.
The 31-year-old was drafted to Alberton Oval from the Bloods in 2008, going on to play 193 games in the AFL.
The South Australian has now ventured back to Hisense Stadium for next year, adding plenty of experience and leadership to West Adelaide's ranks.
“It’s great to be back at the Club where it all started for me. All the boys, especially the younger ones are so eager to learn and improve and hopefully I can aid their development as players," said on the announcement.
"I also hope I can help the older boys that have been at the Club for a while to see some success again.
"I’m excited to be back at West Adelaide working with my brother and so many great people around the place, it’s certainly heading in the right direction and I hope to be a part of sustained success in the future.”
The Bloods amassed a last-place finish this season, recording just the two wins for the year.
West Adelaide have already announced the signing of former Swans and Hawks defender Kaiden Brand for next season, with the 27-year-old also returning to his junior club.