The 45-year-old made 551 appearances for the Robins and replaced Danny Wilson as manager in 2004, before leaving the club the following year.
Tinnion has said that he is happy to be returning to Ashton Gate.
He told the club's official website: "This football club has meant so much to me over the years; I've put my heart and soul into it and it's great to be back.
"This new role is something that really excites me; it's what I enjoy most about football. Discovering good young players and pushing them in their development.
"We need to start by ensuring we have the best Bristol boys at our club and then look further afield as we continue to nurture the players of the future."
Tinnon had been scouting for Premier League side Everton.