Plasmodium malariae is a neglected human malaria parasite despite its global distribution and propensity for persistent, sub-microscopic infections, which are associated with a mild but significant disease burden. Artemisinin-based therapies appear to be efficacious, but the susceptibility profiles of field isolates are largely unknown. We performed ex vivo assays with isolates collected from asymptomatic volunteers in Gabon. The mean concentrations required to inhibit 50% of growth (IC50) with chloroquine (n = 21), artesunate (n = 20), atovaquone (n = 21), and lumefantrine (n = 14) were 7.2 nM, 2.7 nM, 3.1 nM, and 7.4 nM, respectively. Our study provides novel data on the ex vivo susceptibility of P. malariae to several key antimalarials, including the first dataset for atovaquone.