Anum Ishaq masih, in her late teens and from a Christian family, was murdered while she slept in the city of Sialkot southwest of Lahore in the early hours of Sunday.
"Saqib Ishaq masih, 23, killed his sister by smashing her head with a wooden log while she was sleeping," Rana Zulfiqar, the officer in-charge of the police station in Sialkot told AFP.
Rana said the girl was insisting on Saturday that she would marry the man, infuriating her sibling.
The brother has since been arrested and charged with murder after the girl's father filed a case against him.
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Shamoon Gill, a Christian activist, told AFP that honour killings were very rare among the Christian community in Pakistan.
"It has nothing to do with religion but is part of a social issue that is deeply rooted in the eastern societies," he said.