Asama Javed represents the Manningham ward on Bradford Council but Labour recently ruled she would not one of the party’s local election candidates in May.
Halifax will be a hard fought constituency in the General Election with Labour defending a majority of just 1,472.
Coun Javed said: “I cannot be a member of an organisation that breaches all its fundamental principles. There is no fairness, no equality and no justice in the party I have served since I was a teenager.”
But Labour insisted the defection was motivated by Coun Javed’s deselection.
A party spokesman said: “After failing the assessment process to be considered as a candidate in the upcoming local elections, Asama Javed last week decided to leave the Labour Party and resign from the Labour group on Bradford Council.”
He said the decision had been upheld on appeal.