The Buddies have struggled with only two wins from the opening 12 Championship matches and currently sit joint second bottom.
“St Mirren today wish to announce that assistant manager Mark Spalding has left the club by mutual consent,” a statement read.
“On reflection of Saturday’s defeat at Falkirk it was felt that some changes were required going forward and after discussions it was agreed with Mark that he would step down from his role at the club in order for such changes to be made.
“The club wish to thank Mark for putting the club and manager Ian Murray first in this instance and for his hard work on and off the field during his time at the club and wish him well in the future.”
Meanwhile, St Mirren are contesting the red cards shown to Jack Baird and Craig Reid during their 3-0 defeat by Falkirk on Saturday.