"We felicitate the Government and the political parties of Nepal on this achievement. Pakistan is confident that the new Constitution will further cement the foundations of democracy in Nepal," Foreign Office said in a statement.
It said Pakistan's President Mamnoon Hussain and Prime Minister Nawaz Sharif also congratulated Nepali leaders on this historic achievement.
"Pakistan wishes peace and prosperity to the people of Nepal," the statement said.
Nepal yesterday adopted its new Constitution after seven years of painstaking deliberations. The promulgation marked Nepal's transition into a secular and democratic republic.
Nearly 40 people have died in the violent protests. The Madhesi protesters claim they do not have enough representation and their rights have not been protected in the new Constitution.