Results of the arbitration were released Thursday by Actors' Equity Association, which represents stage performers.
"I feel like all you can ask for in this life is to have your day in court and I had that," Piven said in a telephone interview. "The facts were presented and it has been a really long journey for me. I am really happy that we can all move on and that all of the facts, and the medical facts, were heard. That the truth prevailed."
The "Speed-the-Plow" producers, meanwhile, expressed disappointment, saying that while they respect the decision, "we strongly disagree with it. We remain eternally grateful to everyone who helped make the wonderful production of 'Speed-the-Plow' possible, especially the artists who created it, and the many who had to deal with very difficult and trying circumstances."
Piven said there have been misunderstandings about what happened to him explained. The mercury in his system "brought me to my knees," he said, forcing him to rest.
"I was completely exhausted and by the time I ended up in the hospital ... I had arrhythmia (abnormal heartbeat) and the doctor said, 'Your body is definitely trying to catch up and it won't let you - and you need to take care of yourself."'
"I was pretty crippled from the first week of rehearsal on," the actor continued. "Everyone that was involved in the process knows this. And that's the truth that came out."
The National Fisheries Institute, a trade association representing the seafood industry, issued a statement Thursday noting "that no peer reviewed medical journal has ever published any evidence of a case of methylmercury poisoning caused by the normal consumption of commercial seafood in the U.S. This ruling does not change that simple scientific fact."
Piven has wrapped filming season six of his HBO television series "Entourage," in which he plays agent Ari Gold, and he has just completed a lengthy tour promoting his latest movie, "The Goods." Shooting of the seventh season of "Entourage" doesn't begin for a while.
Piven said he considers it a "gift from God" to be lucky enough to make a living as an actor.
"To have worked your entire life and then to have that work ethic be questioned was an interesting turn for me," he said.
"Speed-the-Plow" opened in October to favorable reviews and by the time the production ended its limited engagement in February, it had recouped its $2.26 million production costs.
Three actors - understudy Jordan Lage, Norbert Leo Butz and William H. Macy - followed Piven in the role of movie mogul Bobby Gould. Mamet's three-character play about Hollywood glamour, sex and power, also starred Elisabeth Moss of AMC's "Mad Men" and Raul Esparza.