The separation of East Pakistan in 1971 profoundly demoralized the nation. Under Zulfikar Ali Bhutto's leadership, the Pakistan People's Party (PPP) brought a period of left-wing democracy, with significant initiatives in economic nationalization, covert nuclear development, and cultural promotion. Bhutto, addressing India's nuclear advancements, initiated Pakistan's atomic bomb project in 1972, involving notable scientists like Nobel laureate Abdus Salam.

The 1973 Constitution, created with Islamist support, declared Pakistan an Islamic Republic, mandating that all laws align with Islamic teachings. During this period, Bhutto's government faced a nationalist rebellion in Balochistan, suppressed with Iranian assistance. Major reforms were implemented, including military reorganization and economic and educational expansion. In a significant move, Bhutto yielded to religious pressure, leading to the declaration of Ahmadis as non-Muslims.

Pakistan's international relations shifted, with improved ties to the Soviet Union, Eastern Bloc, and China, while relations with the United States deteriorated. This period saw the establishment of Pakistan's first steel mill with Soviet assistance and intensified efforts in nuclear development following India's nuclear test in 1974.

Political dynamics changed in 1976, with Bhutto's socialist alliance crumbling and opposition from right-wing conservatives and Islamists growing. The Nizam-e-Mustafa movement emerged, demanding an Islamic state and societal reforms. Bhutto responded by banning alcohol, nightclubs, and horse racing among Muslims. The 1977 elections, won by the PPP, were marred by allegations of rigging, leading to widespread protests. This unrest culminated in General Muhammad Zia-ul-Haq's bloodless coup, overthrowing Bhutto. After a controversial trial, Bhutto was executed in 1979 for authorizing a political murder.