Background <p>Second language proficiency has been associated with cognitive processes such as working memory, while speech-in-noise perception requires the integration of auditory processing, attention, and memory-related mechanisms. However, limited evidence is available regarding how L2 proficiency relates simultaneously to working memory capacity and speech-in-noise perception, particularly in young adults with normal hearing. Therefore, this study aimed to examine the effects of L2 proficiency on working memory and speech-in-noise perception in young adults.</p> Methods <p>This comparative cross-sectional study included 44 volunteer participants aged 18–24 years. Twenty-two participants were included in the beginner proficiency group and 22 in the advanced proficiency group. All participants were native Turkish speakers who acquired their second language after the age of six and had normal hearing thresholds. Speech-in-noise perception was assessed using the Turkish Matrix Sentence Test, while working memory capacity was evaluated using the Backward Digit Span Test.</p> Results <p>Across all participants, no significant differences were found between groups in working memory scores (<i>p</i> = .931) or speech-in-noise performance (<i>p</i> = .231). Similarly, no significant differences were observed among female participants for working memory (<i>p</i> = .978) or matrix test performance (<i>p</i> = .939). However, among male participants, the advanced L2 proficiency group showed significantly better speech-in-noise perception, as reflected by lower SNR values in the Matrix Test, compared with the beginner proficiency group (<i>p</i> = .047).</p> Conclusion <p>These findings suggest that L2 proficiency alone may not be a major determinant of working memory capacity or speech-in-noise perception in young adults. However, the observed gender-specific pattern indicates that individual factors may moderate the potential benefits of L2 proficiency for speech processing in adverse listening conditions.</p>