The Scream actor checked himself into rehab back in January for alcohol and depression issues, apparently sparked by his break-up from wife Courteney Cox the previous October.
"Today marks 1 year of sobriety for me," he wrote on Twitter. "I thank God for the strength and guidance and my family and friends for their love and support."
After receiving messages of well wishes from his online following - including congratulatory tweets from celebrity friends Howard Stern, Chaz Bono and Ricki Lake - Arquette added: "Thank you to everyone for your support and kind words of encouragement. I can't thank you all individually but I want 2."
The Dancing with the Stars contestant chose to forgo pain medication following a March car crash in his quest to stay sober.
Arquette admitted that he was "childish" in the wake of his split from Cox.