Over 300 clerics from different schools of Islamic thought issued the decree in Islamabad nearly two weeks ahead of the May 11 general elections, Pakistan Ulema Council chairman Allama Tahir Ashrafi said.
The edict was in marked contrast to the stance taken by the banned Pakistani Taliban, who have described democracy as "un-Islamic" and warned people not to participate in the landmark polls that will mark Pakistan's first democratic transition of power.
Ashrafi said the fatwa contends that voting is an "Islamic obligation" of the people and the action of those who avoid voting will be considered a "sin".
The fatwa further said the democratic system could be changed only through the vote.
Asked about women's rights to vote, Ashrafi said the decree favoured the right to vote for women.
However, the decree said women officials should be deployed at polling stations for women.
Ashrafi asked people to vote in the general election and use their right in favour of good candidates.
If there is no good candidate, then voters can choose a "less bad" option, he said.
All major political parties, including the Pakistan People's Party, PML-N, Pakistan Tehrik-e-Insaf, Muttahida Qaumi Movement, PML-Q, Jamiat Ulema-e-Islam and Jamaat-e-Islami and minorities have backed the decree, he said.
The decree comes at a time when electioneering by major political parties is underway across Pakistan despite threats from the Taliban, who have threatened to target secular parties like the Awami National Party and MQM.
Tehrik-e-Taliban Pakistan spokesman Ihsanullah Ihsan has warned people to boycott the polls.