The girls were seized on Monday, November 17 when armed men stormed their school in Kebbi state shortly after a military detachment left the premises.
The attack triggered a wave of copycat kidnappings in Kwara and Niger states, authorities said.
Nigerian President Bola Tinubu on Tuesday welcomed the girls' release and called on security forces to intensify efforts to free others still held captive.
"I am relieved that all the 24 girls have been accounted for. Now we must put, as a matter of urgency, more boots on the ground in the vulnerable areas to avert further incidents of kidnapping.
"My government will offer all the assistance needed to achieve this," he said.
Mass kidnappings for ransom have become common in northern Nigeria, where armed gangs target schools and rural communities, often overwhelming local security forces.
