The prestigious Ivy League university in Cambridge, Massachusetts, said in a news release that Ms Ardern had been appointed to dual fellowships.
Ms Ardern served as prime minister of New Zealand for more than five years.
She announced she was resigning from public office in January, saying she did not have "enough in the tank".
On Tuesday, Harvard announced that Ms Ardern would be joining their campus in the autumn under dual fellowships at the Harvard Kennedy School.