The President made the declaration in a ceremony held at Aiwan-e-Sadr.
In a news agency report Zardari said that his decision was influenced by the philosophy of his late wife, former Prime Minister Benazir Bhutto, who believed in living for others.
Under the law the sale and unauthorised transplant of body organs is a punishable offence and carries a sentence of up to 10 years in prison.
The law also provides for a regulatory mechanism, including a high-level federal monitoring authority and evaluation committees, for the removal, storage and transplantation of human organs and tissues for therapeutic purposes.
Zardari said that the presence of illegal trade in body organs in Pakistan has drawn the attention of the international community.
He urged parliament and doctors to inform the masses about the issue and urged the doctors to "inform the government in case of any violation and help save precious lives."
"No law can be effective without people's support," the president said and appealed for people's help in countering the illegal trade.