Onomatopoeia constitutes a vital expressive strategy in African literature, yet critical attention to this feature in Dul Johnson’s Deeper into the Night remains scarce. While existing scholarship has largely emphasised the novel’s thematic focus on power, migration, and identity, little has been done to interrogate its phonological aesthetics and the patterned use of sound as vehicles of meaning. This paper, titled phonological functions of Onomatopoeia in Dul Johnson’s Deeper into the Night,” addresses this gap by exploring how Johnson deploys onomatopoeia, repetition, and elongation to enrich the texture of the narrative. Employing a qualitative textual analysis within the framework of literature studies and stylistics, the study examines selected conversations where sound devices dramatise conflict, heighten emotion, and recreate the cadence of phonology. Findings reveal that Johnson’s deliberate use of sound does not only anchor the novel but also provides readers with an auditory experience that reinforces themes of power, violence, and communal memory. The paper concludes that onomatopoeia functions beyond mere stylistic ornamentation; it bridges written and oral performance, reshapes reader engagement, and affirms African literature’s rootedness in oral expressive culture. These insights highlight the need for more scholarly attention to the sonic dimensions of African prose fiction and their phonological implications.