Jemima Khan joined hordes of protesters outside the Pakistan High Commission in London to call for an end to the state of emergency and the release of all political prisoners.
Her ex-husband, the former Pakistan Cricket Captain Imran Khan, was arrested last week alongside thousands of other political opponents after President General Pervez Musharraf implemented the emergency measures on November 3.
About 150 noisy demonstrators gathered calling for "Democracy", "Revolution", and for the General to stand down.
Ms Khan, 33, who has helped start the 'Free Pakistan' movement, a group made up largely of lawyers, journalists, doctors and professionals, stood at the heart of the demonstration with the youngest of her two boys.
The eight-year-old held a picture of his father with the words "Release Imran. Release my Aba" - meaning father.
Ms Khan received a message from her former husband on Saturday, which was smuggled out of the jail where he is being held, to tell their other son, Sulaiman, 11, that he was thinking of him on the boy's birthday.
President Musharraf declared emergency rule, claiming it was necessary because the nation was under threat from militants and an unruly judiciary.
Since then thousands of people including opposition activists and lawyers have been jailed, Supreme Court Judges have been purged, and independent television stations silenced.
The scale of the arrests have left critics to claim the General only declared the state of emergency to hold on to power ahead of upcoming elections.
The General has come under increasing pressure from the international community and yesterday American Deputy Secretary of State John Negroponte, on a visit to Pakistan, called on Musharraf to lift emergency rule and release all political detainees.
