<p>Adoptive cell therapies involving chimeric antigen receptor (CAR)-T cells have been demonstrated to be efficient treatments for hematologic malignancies and have successfully completed clinical translation. While traditional ex vivo T-cell engineering is still limited by challenges such as time-consuming processes, high costs, and poor controllability, as an emerging strategy, in vivo T-cell engineering involves the generation of functional effector T cells directly within patients through several injections of delivery vectors, which can reach cell therapies in days, further reducing costs and increasing scalability. This review logically outlines the technical development and application of in vivo T-cell engineering, with a particular focus on innovations in delivery systems, in which we elaborate on the mechanism and latest advances in viral vector platforms and RNA-based platforms. Furthermore, we analyzed the delivery platforms of multiple therapeutic candidates and their available data, discussing their therapeutic efficacy and safety profiles in both animal models and clinical applications. Although some challenges remain in solid tumor targeting, precise regulation, and manufacturing, increasing preclinical and clinical data have revealed the immense therapeutic potential of in vivo programming strategies across a broad spectrum of diseases.</p>