The Citizens Alliance for Liberty (CXL) nominated for president Oscar Sobalvarro, 68, and Berenice Quezada, 27, for vice president.
Hundreds of supporters chanted "Yes you can," "Freedom" and "Freedom for political prisoners" as CXL made the announcement at a hotel in the capital Managua amid heavy security presence.
Who is Oscar Sobalvarro?
Sobalvarro is a former chief in the right-wing guerrilla groups Contras. Backed by the United States, the rebel groups fought against the Sandinista government led by Ortega in the 1980s.
"That painful war, because it was a war between brothers, could have been avoided if Sandinismo had fulfilled its promise of democracy in 1979 and allowed free elections," Sobalvarro said on Twitter following his nomination.
Sobalvarro said there was hope to remove Ortega from power, as happened in 1990 when "we went out to vote under a dictatorship in a militarized country, but the people, armed only with their vote, proved themselves invincible and we hope that history will repeat itself."
The former commander of the Nicaraguan Resistance group said he would "take on the baton" from those detained, "which is neither easy nor free from risks."
Who is Berenice Quezada?
Quezada was Miss Nicaragua in 2017. She has no known history of a political career.
Following Wednesday's announcement, a photograph of Quezada modeling for an outlet run by Ortega's daughter surfaced on social media platforms, the paper noted. The photograph left observers questioning Quezada's relationship with Camila Ortega.