["Business Strategy and the Environment, EarlyView. ", "\nABSTRACT\nThis study theorises and empirically tests performative purpose alignment theory (PPAT), which conceptualises corporate purpose as a performative artefact materialised through discursive and multimodal signals. To operationalise this, we introduced the SDG–Purpose Alignment Index (SPAI), a computational construct that quantifies the thematic, tonal and stylistic alignment of CEO letters with specific SDG targets. Drawing on 740 CEO letters from 148 publicly listed firms across 10 African economies (2018–2023), we integrate Latent Dirichlet Allocation, domain‐specific sentiment modelling and speech‐act classification within a System‐GMM framework. Findings demonstrate that high SPAI scores predict both superior ESG disclosure and financial performance, positioning rhetorical alignment as a high‐cost governance signal in data‐scarce environments. Moreover, alliteration enhances expressive intent, while excessive repetition undermines authenticity. Visual content modulates these effects: Informative images reinforce narrative credibility, whereas directive visuals erode trust unless rhetorically anchored. Theoretically, this study extends signalling, rhetorical governance and speech act theories by reconceptualising corporate purpose as a linguistically and visually encoded governance mechanism. Methodologically, it offers a replicable tool for measuring SDG alignment in low‐transparency contexts. In practice, it reframes language not as a communicative accessory but as a strategic infrastructure for achieving purpose in the Global South.\n"]