The complex had housed the Prime Minister's Office, the Ministry of Defence and the National Planning Commission of Nepal for decades before being devastated by the 2015 earthquakes.
Some 9,000 people were killed and 22,000 others injured in the twin devastating earthquakes on April 25 and May 12, 2015 in Nepal, Xinhua reported.
Prime Minister K.P. Sharma Oli inaugurated the use of the restored areas of Singha Durbar, whose western part is still being reconstructed.
"Singha Durbar isn't just the main administrative complex, it is also a historically important site of the country," he said during the inauguration.
"The effort to bring the same building into operation after a retrofitting is commendable."
The government had decided to reconstruct the neo-classical structure built in 1908 instead of demolishing it for its archeological value.
Sushil Gyewali, Chief Executive Officer of the National Reconstruction Authority, said that restoration of the Singha Durbar is an important achievement of the reconstruction drive after the 2015 earthquakes.
"The building has been retrofitted using new modern technology keeping the fundamental structure, style and its antique value intact," he told Xinhua.
The Nepali government has spent about 7.4 million dollars so far in rebuilding the 12,461 square meter structure.
Completing the remaining western area of the complex is expected to cost an additional 4.07 million dollars.
Gyewali said the reconstruction of over 90 per cent of the earthquake-damaged 796,245 private houses and a majority of the 7,553 school buildings and hundreds of other public structures, religious and cultural sites destroyed in the 2015 earthquakes have so far been completed.