Mohamed Sebbar made the appeal at a news conference on the eve of an appeal hearing by the victim after a court sentenced one of the girl's three attackers to two years in prison, and the others to 18 months each.
"We hope that justice will be rendered but also that the debate on reforming legislation concerning the protection of minors will be stepped up," Sebbar said in Casablanca.
The now 12-year-old girl from a village near Rabat was raped repeatedly over a period of months, the Jossour Forum of Moroccan Women said in a statement last month.
She was impregnated by one of her attackers, news website Medias24 has reported.
The case has caused an uproar in the North African country, and a petition condemning the sentences, which were announced on March 20, has amassed tens of thousands of signatures.
Last week dozens of demonstrators rallied in the Moroccan capital Rabat to denounce what rights groups have criticized as lenient punishment for the attackers, aged 25, 32 and 37.
Morocco's penal code allows for prison terms of up to 30 years for the charges brought against the three accused, who were also ordered to pay a combined 50,000 dirhams ($4,900) in compensation.
Amina Bouayach, who heads the state-run National Council of Human Rights (CNDH), on Wednesday also urged the government to make "urgent amendments to legislation in order to guarantee the rights of children and their protection against all forms of violence, and namely sexual violence."
Morocco Lawyer Calls for Tougher Child Rape Laws
FILE: Representative illustration of a jail cell door with iron bars. Uploaded Nov. 29th, 2017
CASABLANCA - The lawyer for an 11-year-old Moroccan girl, whose rapists received light sentences that outraged the country, on Wednesday urged authorities to review laws protecting minors.