Thorn, who ran the Nets from 2000-2010 before stepping down last month, will become the head of basketball operations for the Sixers.
General manager Ed Stefanski, who worked under Thorn in New Jersey, will retain his position with the team, sources say, and work under a similar arrangement in Philadelphia.
The rest of the 76ers basketball operations staff is expected to also remain intact.
An official announcement will likely come Thursday.
Thorn, 69, has been associated with professional basketball since the Baltimore Bullets made him the second pick in the 1963 NBA draft after he won All-America honors at West Virginia. He played for four NBA teams over eight seasons before moving into coaching.
He was head coach of the Spirits of St. Louis of the American Basketball Association in 1975-76 and interim coach of the Chicago Bulls in 1981-82, but most of his later career has been in the front office.
Thorn was general manager of the Bulls in the 1980s, then worked as the NBA's executive vice president of basketball operations from 1986 to 2000, when he joined the Nets. He was the NBA's executive of the year in 2002 after the Nets reached the NBA Finals for the first time in their history.