Saleem Shahzad, a long serving MQM member, was suspended by the party leadership this week for violating the party's charter and discipline.
"The party leadership knew I have decided to resign from the basic membership," Shahzad told a private news channel in London while reacting to news of his suspension.
"There is a corrupt lobby in the Muttahida which is against the ideological workers. These elements are involved in extortion, murder, smuggling and other illegal activities," the London-based leader said.
Shahzad, once considered as a most-trusted lieutenant of MQM chief Altaf Hussain, claimed he would also name the people who had made a fortune by illegal means.
"There is a long list of things I want to inform the nation about," he added.