Plasmodium falciparum begins the disease-causing blood-stage of its lifecycle when merozoites invade human erythrocytes. Merozoite invasion is a complex and coordinated process that involves the interaction of many proteins; with the functions of most of these proteins yet to be elucidated. Here we identify and functionally characterise a conserved apicomplexan protein we have named Plasmodium falciparum Cytosolically Exposed Rhoptry Leaflet Interacting protein 1 (PfCERLI1). Using semi-quantitative super-resolution microscopy, we have localised PfCERLI1 to the rhoptry bulb of merozoites and then determined using a range of biochemical techniques that PfCERLI1 is peripherally associated with the cytosolic face of the rhoptry bulb membrane. Pfcerli1 knockouts were unsuccessful, suggesting it is indispensable for blood-stage growth, however the introduction of a glucosamine-inducible ribozyme in the 3’UTR of Pfcerli1 allowed for ~85% reduction in PfCERLI1 protein expression and caused a significant reduction in parasite growth. Knockdown of PfCERLI1 did not lead to a defect in schizont development or rupture and instead was associated with inhibition of merozoite invasion prior to the formation of the tight-junction. Further imaging analysis of the mechanisms of invasion inhibition revealed that PfCERLI1 knockdown caused alterations in rhoptry antigen distribution and processing as well as a defect in rhoptry antigen secretion. Collectively, these data implicate PfCERLI1 as an essential protein involved in P. falciparum rhoptry antigen secretion and function and confirm the utility of our imaging workflow to explore the function of proteins required for malaria parasite invasion of the host RBC.