Cllr Sam Cross was one of the backers of a failed no-confidence motion against council chief Cllr Steve Siddons, which took place on Friday.
At today’s plenary council meeting, Borough Mayor Cllr Hazel Lynskey announced that she had been informed by Cllr Cross that he had resigned from the group.
Due to this change, the board postponed an agenda item on the composition of its committees.
As leader of the independent Cllr Cross group, he was elected chairman of the audit committee earlier this year, a role he is now likely to lose.
Cllr Janet Jefferson has been appointed interim leader of the Independent Group until a permanent leader is elected.
The number of Independent Group members will remain at 10 as Cllr Michelle Donohue-Moncrieff has now joined the group after her departure in early December.
Labor leader Cllr Siddons faced a vote of no-confidence after representatives from two independent groups, including Cllr Cross, and the Tories submitted the motion of no-confidence, claiming he failed to keep promises he had made when he was elected in May. .
After more than an hour of heated debate at Scarborough Town Hall on Friday, the motion was defeated by 26 to 16 votes.