Lynee Stewart, 65, a feisty defender of the poor and unpopular, was accused in the closely watched case of violating an agreement made with the US Justice Department to limit contact between her client, Shaikh Umar Abd al-Rahman, and the outside world.
She could now face up to 15 years in prison.
Stewart on Thursday was convicted of all five counts against her - aiding terrorist activity, conspiring to assist terrorist activity and actually assisting terrorist activity, as well as defrauding the government by breaking her pledge to keep her client from communicating with the outside world and making false statements.
Abd al-Rahman was convicted in 1995 of conspiring to attack US targets, including the 1993 World Trade Centre bombing.
At issue was whether Stewart intentionally helped the jailed Muslim cleric communicate with his followers. Prosecutors said her actions could have led to renewed violence in Egypt.
Stewart denied any wrongdoing and insisted she was doing her job by zealously representing her client.
Stewart's defence lawyer had tried to convince the jury that she was the victim of an overreaching Bush administration that wanted to punish her for her radical views and representation of unpopular clients.