Abstract Methotrexate (MTX) inhibits cell proliferation, which underlies ocular diseases, including intraocular lymphoma and proliferative vitreoretinopathy. However, MTX normally requires bi‐weekly intravitreal injections due to a short half‐life, causing rapid clearance below therapeutic thresholds within 72h. To overcome these limitations, sustained‐release carriers, including poly(lactic‐co‐glycolic) acid‐based implants, were investigated in vitro previously. These systems offer prolonged drug delivery but require relatively large‐gauge surgical implantation, which increases the risk of surgical complications and limits their practical use. In this study, MTX‐loaded liposomes that can be administered via a 30‐gauge cannula are developed, obviating the need for more invasive surgical implantation. This phospholipid‐based liposomal formulation succeeded in enabling sustained methotrexate release at therapeutic levels for over six weeks following a single intravitreal injection, demonstrated in vivo in a large animal pig model. High biocompatibility of this novel liposomal formulation is confirmed through longitudinal retinal structure (optical coherence tomography) and function (electroretinography) assessments. This liposomal formulation of MTX provides a clinically and surgically optimized drug delivery system that allows improved management of intraocular lymphoma and proliferative vitreoretinopathy in the future.