In addition to extending presidential terms indefinitely, the Assembly voted to remove the mandate that a candidate must receive 35% of the vote to be appointed president.
The Assembly approved the legislative changes with a 64 to 25 vote.
The president's Sandinista Party pushed the constitutional change on the basis that Nicaragua needed long-term political leadership to provide stability. The Sandinista leader in the Assembly, Edwin Castro, explained: "This constitution is not the solution for our problems -- poverty or coffee rust -- but it allows us to move forward."
Opposition Independent Liberal Party member Eugenia Sequeira said the amendments "were designed to serve the interests of the current president... It is more of the same in the history of Nicaragua."
President Ortega has been president since 2007. He was previously the country's leader from 1979 to 1990.