The study of the neural basis of syntactic processing has greatly benefited from neuroimaging techniques. Research on syntactic processing in bilinguals has used a variety of techniques, including mainly functional magnetic resonance imaging (fMRI) and event-related potentials (ERP). This paper reports on a functional near-infrared spectroscopy (fNIRS) study on syntactic processing in highly proficient young adult speakers of Portuguese (mother tongue) (L1) and French (second language) (L2). They made a syntactic judgment of visually presented sentences, which either did or did not contain noun–verb agreement violations. The results showed that syntactic processing in both languages resulted in significant activation in anterior frontal regions of the left hemisphere and in the temporal superior posterior areas of the right hemisphere, with a more prominent activation for L2 in some areas. These findings corroborate previously reported neuroimaging evidence, showing the suitability of fNIRS for the study of syntactic processing in the bilingual brain.