Farzana Iqbal was waiting for the High Court in Lahore to open when a group of around a dozen men began attacking her with bricks, said Umer Cheema, a senior police officer.
Her father, two brothers and former fiance were among the attackers, he said. Iqbal suffered severe head injuries and was pronounced dead in hospital, police said.
All the suspects except her father escaped. He admitted killing his daughter, Cheema said, and explained it was a matter of honour. Iqbal had been engaged to her cousin but married another man, Cheema said.
The family registered a kidnapping case against him but Iqbal had come to court to argue that she had married of her own free will, he said.