Wild-type p53-induced phosphatase 1 (Wip1) negatively regulates several tumour suppressor and DNA damage response pathways. However, the impact of Wip1 on haematopoietic stem cell (HSC) homeostasis and aging remains unknown. Here we show that Wip1 is highly expressed in HSCs but decreases with age. Wip1-deficient (Wip1(-/-)) mice exhibited multifaceted HSC aging phenotypes, including the increased pool size and impaired repopulating activity. Deletion of p53 rescued the multilineage repopulation defect of Wip1(-/-) HSCs without affecting cellular senescence or apoptosis, indicating that the Wip1-p53 axis regulates HSC differentiation in a manner independent of conventional p53 pathways. However, p53 deletion did not influence the increased HSC pool size in Wip1(-/-) mice. Interestingly, the expansion of HSCs in Wip1(-/-) mice was due to an mTORC1-mediated HSC proliferation. Thus, our study reveals a mechanism of stem cell aging, in which distinct effects of p53 and mTORC1 pathways on HSC aging are governed by Wip1.