In a social media post on Wednesday, Miss Durkan said she was stepping down following a period of “soul-searching”.
Miss Durkan, who is a barrister, has represented the Foyleside district electoral area since 2019.
“I have concluded that, in light of limitations of party structures, my contribution would be more effectively made outside of council,” she said.
Mrs Durkan is the sister of SDLP assembly member for Foyle Mark H Durkan and the niece of former SDLP party leader and Foyle MP Mark Durkan.
In 2019, Ms Durkan topped the poll with 1,231 first preference votes.
“It has been an honour to serve the people of Derry and Strabane for the past couple of years”, she said.
“I am so grateful to everyone who afforded me that opportunity.”
She added that she would continue to work with all parties, groups and individuals “in the pursuit of a fair deal for the north west of Ireland”.
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