The veteran boss, 66, has called time on his second spell at the club with the Shrews a point above the relegation zone following a poor run of results culminating in Saturday's 3-0 defeat against Rotherham.
Turner said: "It's a very sad decision. It's a club that I've really enjoyed working at, it's a club that gave me my first opportunity in management so I'll always appreciate that and will always be close to the club.
"I just felt it wasn't necessarily just Saturday. I think there's been a sequence of results where for several weeks now I thought I could improve things.
"I thought I was the right man to get the results going and it hasn't materialised so I felt that there was a need for a decision to be made.
"I don't think we could just carry on in the same vein and that decision I reached was I would step down as team manager of Shrewsbury Town."
Turner returned to the club in June 2010, 26 years after he originally left to take charge at Aston Villa, and guided the Shrews to promotion from League Two in 2012.
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