The World Bank has pledged $2bn (£1.2bn) in development aid to Burma for projects including energy supply and healthcare.
Bank president Jim Yong Kim announced the aid during his first visit there.
Burma, also known as Myanmar, has been closed to much of the outside world for many years and is struggling to rebuild its economy.
The bank ceased lending to Burma almost three decades ago when the ruling military junta defaulted on repayments.
Some 70% of the population do not have access to reliable electricity, and improving power supplies is key to the country's development, Mr Kim said.
"We are increasing our support for the huge reform effort under way in Myanmar because we want to help the government bring benefits to poor people even more quickly," Mr Kim said.
"Expanding access to electricity in a country like Myanmar can help transform a society. Children will be able to study at night, shops will stay open, and health clinics will have lights and energy to power life-saving technology. Electricity helps brings an end to poverty."
The Washington-based bank closed its office in the main city of Rangoon (also known as Yangon) in 1987 and ceased new lending after the junta stopped making payments on debts worth hundreds of millions of dollars.
Burma last year cleared its arrears to the World Bank and the Asian Development Bank with the help of a Japanese bridge loan, enabling the two lenders to resume assistance to the country.
Since taking control of a civilian government in 2011, President Thein Sein has started political and economic reforms, resulting in the lifting of international sanctions.
Critics, however, have said that the pace of change is too fast, and there have been outbreaks of violence across the country.
But with sanctions on Burma having been rolled back, overseas firms are lining up to invest in the country, which not only has huge natural resources, but lies in a strategic location between China and India.
The aid programme announced by the bank includes $200m to help Burma achieve universal health coverage by 2030.