Gathered in a coalition called Cap 20-21, 18 parties launched “an appeal for civic responsibility from all the political forces in Niger… to join the final combat.”
Cap 20-21 was launched last September with the aim of backing the candidate with the best chance in the second round.
Opposition parties in Niger have urged candidates preparing for the second round of presidential elections on February 21 to rally behind former president Mahamane Ousmane, the runner-up to Mohamed Bazoum in last month’s first round.
The manifesto was first read out on Monday to more than 3,000 people in Niamey’s main sports arena.
Mohamed Bazoum, a former interior minister supported by outgoing President Mahamadou Issoufou, took a strong lead in the first round of voting on December 27, winning 39.33 percent of ballots cast.
Ousmane won 16.99 percent in a crowded field of 30 candidates.
Both frontrunners will need to haggle with other candidates to secure their support, a process likely to be complicated in the poor Sahel country where alliances are fickle.
Issoufou is voluntarily standing down after two five-year terms in office.
Handing over to another democratically-elected newcomer will be a first in Niger after a history studded with coups d’etat since independence from France in 1960.
The movement fielded four other candidates in the first round. The highest score among these went to Ibrahim Yacouba, with 5.38 percent.
It has also attacked what it calls irregularities in the first round and threatened not to recognise the results of the runoff if it is not “transparent and honest.”
But a government statement issued late Monday said that five Cap 20-21 members would take up seats on the Independent National Electoral Commission (CENI), ending a three-year boycott of the electoral board by the opposition.
A Cap 20-21 leader, Amadou Ali Djibo, told AFP on Tuesday that the move was spurred by the need to “protect” the results of the runoff after “numerous frauds in the first round.”
On Sunday, 10 other candidates formed a separate movement called the Alliance of Candidates for Change (ACC). They included Niger’s former military ruler Salou Djibo (2010-2011), who handed over power to Issoufou. The ACC’s candidates garnered less than 10 percent in the first round.