Turnbull stood down after Saturday's 2-1 home defeat at the hands of Witton Albion, a result which left the club bottom of the Northern Premier League with only one win (three points) from their opening eight fixtures.
A statement issued by the club said: “Morpeth Town can confirm that manager Stephen Turnbull has stepped down from his position with immediate effect.
“Following today’s (Saturday’s) 2-1 defeat at home to Witton Albion, Turnbull offered his resignation to the Chairman, Ken Beattie, and CEO, Mark Hedley.
“We would like to thank Stephen for all the hard work he has put in as a player and manager during his time at the club and wish him well for the future.
“I’ve got the greatest respect and regard for Stephen and he has been extremely unlucky with a number of factors including Covid-related disruption,” said Beattie.
“He has been a tremendous player and ambassador for Morpeth Town. He has high standards and will continue to do well going forward.
“We look forward to welcoming him back to Craik Park in the near future with a warm welcome.”
After a run of poor form, Morpeth had been hoping to bounce back with a win against Witton Albion.
Jeff Henderson smashed home for the Highwaymen to give them the perfect start but the visitors hit back with a goal in each half from Sam Saunders, who was making his debut for the visitors.