The Harderian gland is a large cephalic gland present in most groups of terrestrial vertebrates. Although this gland has been the focus of numerous studies for over 300 years, its physiological function has remained largely unresolved. In the red-sided garter snake Thamnophis sirtalis parietalis, the Harderian gland appears to be an integral component of the vomeronasal chemosensory system both by facilitating the detection of non-volatile chemical signals and as a component of the extracellular immune system. The Harderian gland of T.s.parietalis secretes its contents solely into the lumen of the vomeronasal organ and exhibits sexually dimorphic seasonal structural changes coinciding with a mutually exclusive shift in behavior from spring mating to summer feeding. Using an integrated approach employing high throughput RNA-sequencing paired with protein mass-spectrometry, we examined the functional characteristics of the Harderian gland transcriptome as well as identified and functionally characterized the proteins present in vomeronasal secretions to describe a sexually dimorphic and seasonally variable role of this tissue. The Harderian gland showed high expression of genes associated with lipid-binding proteins and others involved in the extracellular immune system. Proteins identified in the fluid of the vomeronasal organ showed an abundance of lipid-binding proteins and extracellular immune proteins. Antimicrobial properties of vomeronasal secretions were demonstrated via in-vitro bacterial killing assays. A protein of particular interest was identified as a lipid-binding protein of the lipocalin family and a likely candidate for a putative pheromone-binding protein facilitating the detection of female sexual attractiveness pheromone.