This study investigates the developmental trajectory of simultaneous bilingualism in an Iranian child exposed to English from birth within an English as a Foreign Language (EFL) context. Addressing the limited research on early bilingual acquisition in non-English-speaking environments, the study aims to identify key linguistic milestones and challenges encountered during the bilingual development process. Employing a longitudinal case study design, the research observed a two-and-a-half-year-old Iranian boy over a 32-month period. Data were collected biweekly through direct observation of the child’s natural interactions in a home setting where Persian was the dominant language and English was introduced as a second language. Language development was systematically recorded and analyzed to track progress across phonological, lexical, and syntactic domains. Findings revealed three distinct phases of bilingual development, marked by increasing complexity in sentence formation, interrogative structures, and lexical diversity. Notable linguistic behaviors included code-switching, overextensions, and effective use of conjunctions. The study also identified persistent challenges such as vocabulary acquisition delays, grammatical inconsistencies, and pronunciation difficulties, exacerbated by limited English exposure outside formal instruction. The results underscore the feasibility of simultaneous bilingualism in EFL contexts when supported by consistent input and interaction. These insights have implications for early childhood education, bilingual curriculum design, and parental strategies in non-English-speaking regions. Future research should explore comparative outcomes across diverse EFL settings and examine long-term cognitive and academic impacts of early bilingual exposure.