The accused, identified as 19-year-old Saeed Anwar, had been upset at his sister, Mismat Musarrat, 18, for marrying Qaiser, 25.
The incident took place in Nagyal in Rawalpindi's Gujjar Khan tehsil and police described it as an 'honour killing', Dawn newspaper reported.
The Station House Officer Ishtiaq Masood Cheema said the suspect had been waiting for an opportunity to kill the couple ever since they married a few months ago without the consent of his family.
He later tried to flee the scene, but was apprehended by the police along with the murder weapon.
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Cheema said police have booked Anwar for a double murder. Police will present him in court tomorrow to seek physical remand. The bodies of the victims have been shifted to a local hospital for a postmortem.
Last month, a newly-wed couple in Sindh province who married without the consent of their elders were killed allegedly on the orders of a jirga (village elders).
Activists say around a thousand Pakistani women fall victims to so-called honour killings every year in which the victims, mostly a woman, are usually killed by a relative or on the orders of village elders for bringing dishonour to the family or the community.
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