The two approached the victim yesterday when she was at a bus stop in Lahore and threw acid on her. They fled the scene after the incident.
The victim was rushed to a nearby hospital where her condition is stated to be critical.
Ali Raza and his accomplice threw acid on the girl, said Superintendent of Police Awais Malik.
"Raza had allegedly raped her sometimes ago and was at large," he said, adding that it appeared the accused wanted to stop the victim from pursuing the case against him.