According to officials, the blackout started after midnight when a transmission line connecting a privately-run power plant to the national grid was damaged.
Electricity was cut off across major cities in Pakistan, including the capital Islamabad, in one of the worst power failures the country has experienced.
An estimated 80 percent of the country was affected by the power breakdown, said a senior official at the National Grid station in Islamabad.
The blackout also caused disruption at Lahore's international airport and two nuclear power plants were reportedly offline.
As electricity was slowly restored across the majority of the country, the minister of state for water and power, Abid Sher Ali, issued an apology, blaming the power cut on a militant attack on a transmission tower in the south western Baluchistan province, reported AFP News.
Later, a spokesman for the national power company said: "Electricity has been restored in all parts of the country. Some 6,000 megawatts of electricity has been added to the national system and within a couple of hours distribution will be normal."
Since Pakistan's electricity distribution is intricately delicate, a fault at one section can cause a ripple effect with breakdowns of power generation.
Residents across Pakistan usually endure long hours of electricity outages nearly everyday.
Pakistan was also hit by a major fuel shortage earlier last week when Pakistan State Oil, which supplies 80 percent of the country's oil, was refused further credit from banks directly affecting its imports.