Miller revealed his sexual orientation in an open letter to the organisers of a film festival in Russia, rejecting an offer to attend the event due to the conservative country's anti-gay laws.
He wrote, "Thank you for your kind invitation. As someone who has enjoyed visiting Russia in the past and can also claim a degree of Russian ancestry, it would make me happy to say yes. However, as a gay man, I must decline."
Neil Patrick Harris and Matt Bomer are among the openly gay stars who congratulated the actor on his move, and now Purcell has also saluted Miller.
He tells UsMagazine.com, "As a friend and someone I care for deeply, I am very proud of Wentworth. I wish him much happiness and peace. I applaud his courage and his stance against a wrongful, archaic ideology."
Purcell played Miller's older brother on the hit jail drama from 2005 to 2009.