Under sanctions for human rights abuses, Ortega himself had proposed the change, which also increases the Central American country's presidential term from five to six years.
Ortega, 79, has engaged in increasingly authoritarian practices, tightening control of all sectors of the state with the aid of his powerful wife, 73-year-old Vice President Rosario Murillo in what critics describe as a nepotistic dictatorship.
The ex-guerrilla had first served as president from 1985 to 1990, returning to power in 2007. Nicaragua has jailed hundreds of opponents, real and perceived, since then. Ortega's government has targeted critics, shutting down more than 5,000 NGOs since 2018 mass protests in which the United Nations estimates more than 300 people died. Thousands of Nicaraguans have fled into exile, and the regime is under US and EU sanctions. Most independent and opposition media now operate from abroad.
Ortega and Murillo accuse the Church, journalists and NGOs of having supported an attempted coup d'etat, as they describe the 2018 protests. The change also allows for stricter control over the media and the Church, so they are not subject to "foreign interests." And it gives the co-presidents the power to coordinate all "legislative, judicial, electoral, control and supervisory bodies, regional and municipal" -- formerly independent under the constitution.
The Geneva-based UN human rights office (OHCHR) in its annual report on Nicaragua warned in September of a "serious" deterioration in human rights under Ortega. The report cited violations such as arbitrary arrests of opponents, torture, ill-treatment in detention, increased violence against Indigenous people and attacks on religious freedom.
"Everything in the reform is what has actually been happening in Nicaragua: a de facto dictatorship," Dora Maria Tellez, a former comrade in arms of Ortega turned critic, told AFP from exile in the United States. When it was proposed by Ortega earlier this week, Organization of American States secretary general Luis Almagro described the amendment as "an aberrant form of institutionalizing the marital dictatorship."