Kulsoom Nawaz stood in place of her husband Nawaz Sharif, who was disqualified from office in July.
She won 61,254 votes, 14,188 more than her nearest rival, local media say.
The vote was seen by both the ruling PML- N party and the opposition as a referendum on the Supreme Court's decision to disqualify Mr Sharif.
Ms Nawaz is currently in London for cancer treatment. Her daughter, Maryam, spearheaded the campaign for the PML-N party in her absence.
"This is not an ordinary victory," Maryam told party supporters after the unofficial results were declared. "You have defeated not only people who were in the field but also those who are invisible."
She said winning her father's former seat in the family's hometown showed that people had rejected the "unjust decision" to disqualify her father.