On February 9, Imran was produced before ATC which chose to hold the trial in jail owing to security issues.
Ali was sentenced on four counts - murdering a child, kidnapping a child, raping a minor and committing an unnatural act with a minor.
"It was a fair trial in which the suspect was given a chance to defend himself", Qadir said, adding the ATC has awarded the sentence to the accused only in the case of the seven-year-old girl.
"When he was read the charges, we asked the court to let Imran Ali deliberate the matter for 40 minutes", the prosecutor said. According to Section-25 of Anti-Terrorism Act, the convict can challenge the verdict within 15 days.
Zainab's father was in court to hear the verdict, amid heavy security.
As per the orders of Chief Justice of Pakistan Saqib Nisar, Punjab Prosecutor General Ahtesham Qadar personally attended all the hearings of the case.
The country's special anti-terrorism court in Lahore convicted Mohammad Imran Ali after Zainab Ansari's body was found in a trash dump in Kasur district near Lahore, in Punjab province, on January 9, two days after she disappeared.
Her case was the twelfth such incident to occur within a 10-kilometre radius in the city over a 12-month period.
Two protesters died in rioting demonstrating against the police's delay in finding the killer. Ali was arrested on 23 January.
Imran had reportedly even confessed to other crimes on further investigations. A total of 56 witnesses were named in the case.
The court had on Monday indicted Imran in the case.
Zainab's brutal murder sparked anti-government demonstrations across the country. The Lahore High Court had given seven days for completion of the trial. The apex court also expressed satisfaction on the performance of police.
One million rupees of the fine would be given in compensation to Zainab's family, public prosecutor Abdul Rauf Wattoo said. Residents had done massive protests after Zainab's body was found.
On January 9, a police constable recovered her body from a heap of rubbish.
The arrest brought to light eight more such killings and many Pakistanis have demanded he be publicly executed. During the search, DNA tests were conducted on more than 1,100 people living in the area. "The suspect had also confessed to the killing of eight other girls". Ali is also accused of murdering Eman Fatima. The post-mortem of the minor revealed that she had been raped before being murdered.