Clark parts company with the Club alongside assistant Paul Stephenson following a run of six straight defeats.
The former Newcastle midfielder arrived at Croft Park last summer to succeed Darlington-bound Alun Armstrong.
Spartans lie second from bottom in Vanarama National League North- six points from safety.
A statement on the Club website read: “It is with regret that Blyth Spartans announce that manager Lee Clark and assistant Paul Stephenson have left the Club by mutual consent.
“We would like to thank Lee and Paul for all their efforts and professionalism during their time at the Club.
“Michael Nelson will take charge of team affairs for the remainder of this season”.
Photo Credit: Kris Hodgetts