Apicomplexans are a phylum of obligate intracellular parasites that, by their very nature, rely on nutrient scavenging from their hosts for survival. Nutrient transporter proteins are key to nutrient scavenging, although few transporters have been characterized in these parasites. The Novel Putative Transporters (NPTs) are an apicomplexan-specific family of transporter proteins. Here, we characterize NPT1 from the apicomplexan Toxoplasma gondii (TgNPT1). Genetic disruption of TgNPT1 revealed that this transporter is essential for parasite growth and virulence. Surprisingly, we found that TgNPT1 mutants grew normally in a medium containing increased arginine levels, implicating TgNPT1 in arginine transport. Direct measurements of arginine uptake into T. gondii parasites revealed a reduction in arginine uptake by parasites lacking TgNPT1. Expression of TgNPT1 in Xenopus laevis oocytes resulted in a marked increase in arginine uptake. These data are consistent with TgNPT1 being an arginine transporter. Expression of TgNPT1 is up-regulated in medium containing lowered arginine levels, suggesting expression of this transporter is tightly regulated to modulate arginine uptake into the parasite. Our findings highlight the importance of arginine uptake for T. gondii growth, identify the first amino acid transporter in apicomplexan parasites, and suggest that NPTs may be an apicomplexan-specific family of amino acid transporters.