The incident took place at Garnavathi village in Kalanaur area.
After killing the girl, the accused, identified as Amit, attempted to commit suicide by shooting himself but he was rushed by some villagers to PGIMS where his condition is stated to be out of danger, police said, adding that a case of murder has been registered against the youth.
According to police, the wedding of the girl was to be solemnised on July 13.
"We are probing the case from various angles...Statement of Amit is yet to be recorded," a police official said.