Microneedles (MNs) are micron-scale structures that can painlessly penetrate the skin barrier to facilitate drug delivery, biomarker sampling, and biosensing. During MN fabrication, although conventional molding techniques allow for large-scale production, they exhibit inherent limitations in the rapid and personalized customization of geometric structures—parameters that are critical determinants of the biomedical functionality and performance of MNs. As a next-generation manufacturing paradigm, 3D printing offers novel opportunities for the development of personalized and intelligent MNs, leveraging its high precision, design flexibility, and integrated fabrication capabilities. This article reviews the different types of MNs and their geometric characteristics, systematically summarizes the applications, advantages, and limitations of mainstream 3D printing technologies in MN fabrication, and focuses on recent research advances in 3D-printed MNs for drug delivery, biomarker extraction, and biosensor construction. Furthermore, it provides an in-depth overview of the application potential of 3D-printed MNs in the treatment of various diseases. The article also discusses the emerging integration of 4D printing and artificial intelligence (AI) within this domain. Finally, we conclude with a summary and propose potential directions for future research.