James Arthur Ray, an Oprah-endorsed motivational speaker who spent two years in prison for manslaughter after the 2009 deaths of three people in a sweat lodge, the culmination of a three-day spiritual program he ran in the Arizona desert, died on Jan. 3 in Henderson, Nev. He was 67.

His brother, Jon Ray, announced the death on social media. He did not say where in Henderson Mr. Ray died or cite a cause, but he did say the death was unexpected.

Mr. Ray was struggling to succeed as a motivational speaker when he appeared in “The Secret,” a 2006 documentary made by the Australian television producer Rhonda Byrne. The “secret,” which Mr. Ray and others espoused, was the idea that positive thinking can literally make the world shift in your favor.

Things began to move quickly for Mr. Ray. He appeared on Oprah Winfrey’s show, where she lavished praise on him. Within months he was standing in front of sold-out crowds of hundreds, then thousands. In 2008 he published “Harmonic Wealth: The Secret of Attracting the Life You Want,” written with Linda Sivertsen, which reached The New York Times’s best-seller list.

He was, Fortune magazine declared in 2008, “the next big thing in the highly competitive world of motivational gurus.”