The cyber firm developed a spyware product called Pegasus that enables government agencies and law enforcement to hack smartphones and read data on the devices.
Several reports surfaced over the summer revealing that Pegasus was used by various countries to target human rights activists and journalists.
The lawsuit also includes NSO Group's parent company Q Cyber Technologies.
“State-sponsored actors like the NSO Group spend millions of dollars on sophisticated surveillance technologies without effective accountability. That needs to change,” Craig Federighi, Apple’s senior vice president of Software Engineering, said in a statement.
Apple also announced a $10 million contribution to organizations involved in cyber surveillance research and advocacy.
Earlier this month, the United States Commerce Department announced that the NSO Group was being added to a federal trade blacklist for acting "contrary to the foreign policy and national security interests of the US."