According to police, Kulsoom Bibi had come to the Multan High Court, some 350-km from Lahore, for a hearing along with her husband Rafaqat when her brother 17-year-old Zulqarnain reached there and opened fire on them.
Kaloom died on the spot while Rafaqat succumbed to his injuries in a hospital. The couple's lawyer also suffered bullet injuries who was shifted to a hospital where his condition is stated to be critical.
Kalsoom recently had contracted marriage with Rafaqat against the will of her family.
The officials termed the incident "an act of honour killing".
Zulqarnain, after killing the couple, surrendered himself before the police and confessed to his crime.
"I have killed my sister and her lover for disgracing the family honour," Multan police official Raza Ali quoted him as saying.
Last month, a 20-year-old Pakistani woman and a man she was having an affair were hacked to death allegedly by her father and brother in Karachi.
Hundreds of women are murdered every year in Pakistan, often by their own relatives, for marrying against their families' wishes.
Last year, over 1,100 women were killed in Punjab in the name of honour.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)