The 54-year-old had recently started a new job at Peterborough United but has now stepped into a big role with League Two’s basement side.
Turnbull will officially be called the club’s chief operating officer but the Iron have confirmed that he will be taking on the chairman’s roles.
Scunthorpe lost 1-0 at Forest Green Rovers yesterday and are 13 points from safety with six games to play.
Turnbull made over 150 appearances for Rovers during two spells in the late 80s and early 90s and in recent seasons has featured on BBC Radio Sheffield as a pundit during games.
He also has a long affinity with the Iron and made 52 league appearances for them between 1995 and 1997.
He also served as the club’s head of community for 17 years and had two spells as their chief scout. He also returned in 2016 as head of recruitment.
Former chairman Peter Swann stepped down with immediate effect last Thursday with the club facing relegation to the National League.
Turnbull joined Peterborough at the beginning of March. He was brought in by former Rovers boss Grant McCann to fill a newly-created role of head of opposition scouting and analysis.