He joins Brendon McCullum as the second overseas player in the side.
Hastings had represented Australia in 29 ODIs and 9 T20Is.
He will fill the second international spot in the BBL franchise's 18-man roster.
Earlier today, he confirmed that he will be playing in the PSL.
The Perth-born cricketer expressed his delight and is looking forward to working with Voges.
Both of them are currently busy playing in the ongoing Test series against India.
Mills has to clear the fitness test as he suffered a quadricep strain which ruled him out of the T20 Blast in England.
De Villers is likely to play in the upcoming season with most of the teams in the race to sign him.
Johnson will be turning 37 as the Australian summer begins.
The eighth season will kick off on December 19.