The suspect, identified as a man from India's eastern state of Bihar, was taken into custody late Sunday, The Wall Street Journal reported.
Police arrested another man Friday. He allegedly rented the apartment where the girl was held captive and sexually abused.
The first suspect allegedly named the second arrested man as an accomplice, said Rajan Bhagat, a Delhi police spokesman.
Neither suspect has been charged in the case.
The incident comes after gang rape of a 23-year-old student on a bus in New Delhi sparked protests in India and brought global attention to how women are treated in the country.
"I believe India is in a unique moment in history to address the issue of violence against women," said Rashida Manjoo, the U.N. Special Rapporteur for violence against women, said in a statement ahead of her visit to India to investigate the recent case.