ISLAMABAD, Pakistan — Asma Jahangir, a leading Pakistani rights activist, fearless critic of the military’s interference in politics and a staunch defender of the rule of law, died on Sunday in Lahore. She was 66.

The death was confirmed by her daughter Munizae Jahangir, who said the cause was a heart attack.

Ms. Jahangir, a human rights lawyer, had a reputation for speaking truth to power and defending the weak and the marginalized and women and minorities against injustice. She gained international acclaim for being the conscience of a country where liberal, secular voices have continuously been under threat.

She was the founding chairwoman of the Human Rights Commission of Pakistan, an independent group, and was a trustee of the International Crisis Group. She won international awards and served as the United Nations rapporteur on human rights and extrajudicial killings.

Ms. Jahangir never minced words while defending democracy and human rights, despite threats to her life, both from military dictators and militants. She championed the rights of religious minorities — especially those who were charged under the country’s blasphemy laws — and women and men killed in the name of honor.