Donor human milk is the recommended alternative for feeding preterm or low birth weight infants when the mother’s own milk is unavailable or not in sufficient quantity. Globally, the needs of vulnerable infants for donor human milk exceed the supply. This review aimed to identify the factors impacting the sustainability of human milk donation to milk banks. A systematic review of the literature was performed on eight databases to retrieve articles published until December 2021. The study protocol is available in PROSPERO (#CRD42021287087). Among the 6722 references identified, 10 studies (eight quantitative observational and two qualitative) met the eligibility criteria for a total of 7053 participants. Thirty factors influencing the sustainability of the donations to milk banks were identified and categorized as follows: (1) donation duration, (2) donors’ infant features (e.g., gestational age, birth weight), (3) donors’ features (e.g., socio-demographic characteristics, milk donation history), and (4) factors related to the milk bank and health care systems (awareness and support). The available evidence suggests that larger volumes of donated milk are associated with a longer duration of donation, as are early donation, previous milk donation, and donors with an infant of smaller weight and gestational age. Supporting and encouraging early donation and recruiting donors with infants of low birth weight and low gestational age could support longer donation times and greater volumes of milk donated. To identify efficient strategies and to draw appropriate recommendations to improve donor milk access, future studies should further explore the issues of the sustainability of human milk donation to milk banks.