According to the Grain Size Accommodation hypothesis (Lallier & Carreiras, 2017), learning to read in two languages differing in orthographic consistency leads to a cross-linguistic modulation of reading and spelling processes. Here, we test the prediction that bilingualism may influence the manifestations of dyslexia. We compared the deficits of English monolingual and early Welsh–English bilingual dyslexic adults on reading and spelling irregular English words and English-like pseudowords. As predicted, monolinguals were relatively more impaired in reading pseudowords than irregular words, whereas the opposite was true for bilinguals. Moreover, monolinguals showed stronger sublexical processing deficits than bilinguals and were poorer spellers overall. This study shows that early bilingual reading experience has long-lasting effects on the manifestations of dyslexia in adulthood. It demonstrates that learning to read in a consistent language like Welsh in addition to English gives bilingual dyslexic adults an advantage in English literacy tasks strongly relying on phonological processing.