This study examined the role of social context in the expression of the bilingual cognitive advantage in 145 bilingual university students. All participants mastered Arabic as their native language (L1), but half were highly proficient in French (high L2 group), whereas half were less proficient (low L2 group). A color-word Stroop test with incongruent, congruent and neutral stimuli was administered in single language blocks (Arabic or French words) or in a mixed block (Arabic and French words), either under social presence, or alone. Stroop interference was analyzed to assess the cost of resolving conflict in incongruent trials and was compared across groups and experimental conditions. If bilingualism comes with a cognitive advantage, a reduction of interference in high (vs. low) L2 proficient subjects is to be expected. Analysis revealed that interference was significantly reduced in high L2 group, but only under the single language condition. Furthermore, whereas social context and sex had no main effects, analysis revealed a significant 4-factor interaction between L2 proficiency, linguistic context, social context, and sex. Social presence further reduced interference (social facilitation) in high L2 proficient females, but not in males. Overall, the results suggest that mastering a second language comes with cognitive advantages which adapt dynamically to social and linguistic contexts in a sex-dependent manner. We argue that advancing bilingualism research requires more attention to the social environment.