The USD 500 million will be provided by the US government's Millennium Challenge Corporation (MCC), a foreign aid agency set up by the US Congress in 2004. It is independent from the State Department and the USAID.
The Nepal government has committed to contribute an additional USD 130 million, the US embassy said in a statement.
The compact - MCC's larger grant programme - includes two projects.
The electricity transmission project is designed to expand Nepal's power sector, which includes a second cross- border transmission line to facilitate electricity trade with India.
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The compact is likely to be signed by both governments in September.
"I am pleased to announce the Millennium Challenge Corporation Board of Directors' approval of the Nepal Compact," said its acting CEO Jonathan Nash.
"This compact with Nepal focuses on the power and transportation sectors to improve regional connectivity, spur private investment, drive growth, and reduce poverty," Nash said.