The formation of membrane contact sites (MCSs) between intracellular pathogens and host organelles is a common consequence of infection. We previously found that the human parasite Toxoplasma gondii forms contact sites with host mitochondria and drives the shedding of their outer membrane. Here, we investigate the molecules that mediate the MCSs between Toxoplasma and host endoplasmic reticulum (ER). Although these MCSs were first described in 1968, the proteins mediating this contact remain unknown. To this end, we developed a split-GFP based sensor wherein GFP reconstitution indicates successful formation of contact sites between the pathogen and host organelles. To validate our sensor for FACS based CRISPR-Cas9 screening, we first applied it to monitor Toxoplasma-mitochondria MCSs and as expected found that our sensor reconstituted GFP at these contact sites, but failed to do so in the absence of the mitochondrial tether TOM70 or its Toxoplasma counterpart MAF1. To identify the proteins that tether the ER to the parasite vacuole in an unbiased manner, we adapted our sensor to Toxoplasma-ER MCSs and performed a genome-wide loss of function CRISPR screen. Our candidate ER tether suggests a conserved mechanism by which pathogens contact diverse host organelles. Defining the molecules that mediate pathogen-organelle MCSs will enable us to determine their function during infection and enhance our understanding of contact site biology in general.