The Central American country last month announced plans to attach itself to the application by Pretoria, which brought Israel before the International Court of Justice.
South Africa, long a vocal supporter of the Palestinian cause, has accused Israel of breaching the 1948 U.N. Genocide Convention over its military campaign in Gaza, sparked by the October 7 attacks by Hamas.
Managua filed its own application on January 23, which the Hague-based ICJ confirmed on Thursday.
"In its application for permission to intervene, Nicaragua states that it 'has interests of a legal nature that stem from the rights and obligations imposed by the Genocide Convention on all State Parties," the ICJ said.
Managua said its decision flowed from "the universal character both of the condemnation of genocide and of the cooperation required 'in order to liberate mankind from such an odious scourge,' " the court said in a press release.
Two weeks ago, the court's judges handed down a set of emergency measures, saying Israel must prevent genocidal acts in its war with Hamas but stopped short of calling for an end to the fighting.
Nicaragua in its own application called on judges to rule that Israel "has breached and continues to breach its obligations under the Genocide Convention" and to "cease acts or measures which would be capable of killing or continuing to kill Palestinians."
The case to decide whether Israel was actually breaching the Genocide Convention with its military campaign was likely to still take months, if not years.
Israeli Prime Minister Benjamin Netanyahu has rejected the case as "outrageous" and hinted that Israel would not abide by any ruling saying "no one will stop us," not even a verdict in The Hague.
Hamas in early October launched an unprecedented attack that resulted in the deaths of about 1,160 people in Israel, mostly civilians, according to an AFP tally based on official Israeli figures.
Vowing to eliminate Hamas, Israel launched relentless air strikes and a ground offensive that has killed at least 27,840 people, mostly women and children, according to the health ministry in Hamas-ruled Gaza.
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