Mutahida Qaumi Movement (MQM) leader Saleem Shahzad was arrested on Monday at Karachi's Jinnah International Airport upon his return to Pakistan after 24 years.
Senior Superintendent Police Malir Rao Anwar confirmed the report to Dawn News.
Shahzad, a founding member of the MQM-London, had been living in London since 1992 and announced his return on Twitter on Sunday. He returned to Pakistan on a flight from Dubai.
"Reaching #karachi inshallah Monday morning may Allah Bless our city,province and my country Ameen," Shehzad tweeted yesterday.
Arrest warrants were issued for Shahzad in 2016 for the 10th time by an Anti-Terrorism Court in Karachi in a case related to providing treatment and shelter to alleged terrorists.
Upon Shahzad's arrival at Karachi airport, the Federal Investigation Agency (FIA) contacted the police.
Speaking to Geo News before departing from Dubai, Shahzad had said he would announce his next political move after arriving in Karachi following consultation with friends and family.