Transdermal drug delivery offers several advantages over oral and injectable routes, including controlled release, avoidance of first-pass metabolism, and improved patient compliance. Solid lipid nanoparticles (SLNs) have emerged as versatile nanocarriers owing to their biocompatibility, stability, and ability to encapsulate a wide range of drugs. Incorporating SLNs into polymeric transdermal films enhances drug permeation, provides sustained release, and improves therapeutic efficacy by combining lipid-based nanocarriers with flexible, adhesive matrices. This review summarizes formulation strategies, physicochemical properties, and mechanisms of drug permeation associated with SLN-loaded transdermal films. Particular focus is given to polymer–lipid interactions, release kinetics, and skin penetration pathways. Recent applications include delivery of antihypertensives, antidiabetics, analgesics, and phytoconstituents, demonstrating their potential across diverse therapeutic areas. Challenges such as stability, large-scale production, and regulatory considerations are also highlighted. Overall, SLN-based transdermal films represent a promising platform for controlled drug delivery with opportunities for clinical translation.