Investigators tell Action News that there was a party inside at the time with several juveniles in attendance
Police say Terrence Maxwell, 20, of the 1500 block of North Rosalie Street, was playing with a handgun when it discharged.
The 13-year-old girl was hit once in the chest.
She was rushed to Saint Christopher's Hospital and has since been treated and released.
An arrest warrant has been issued for Maxwell.