The Oscar-winning actor was found dead in his West Village, Manhattan apartment on Sunday afternoon (2 February), according to law enforcement officials.
A cause of death has yet to be confirmed although police have said it is suspected to be a drug overdose.
A friend raised the alarm on Sunday afternoon. Emergency services found the actor on the floor of his bathroom.
He leaves behind his long-time partner Mimi O'Donnell, a costume designer, and their three children, daughters Willa and Tallulah, and son Cooper.
Seymour Hoffman won an Academy Award for his role as Truman Capote in 2005's Capote. His varied career included critically-acclaimed roles on stage and appearances in movies including Mission Impossible III, The Master, Cold Mountain, Along Comes Polly, The Talented Mr Ripley and The Big Lebowski.
Most recently he was working on The Hunger Games franchise, filming the role of Head Gamemaker Plutarch Heavensbee in Mockingjay.