English language is used as the medium of teaching in Ghanaian schools from Basic to the tertiary levels. Students at all stages of education are taught the content of school subjects through the use of the English language. As a result, how well students perform academically is mainly determined by their proficiency in English language. This paper therefore examined the relationship between English language proficiency and academic performance in Biology. The study employed a hybrid of ex-post facto and correlational research designs to determine the extent at which science students’ performance in English language correlates with their academic performance in Biology. Secondary data in the form of Terminal examination scores and 2019 West African Senior Secondary School Certificate Examination (WASSCE) results in English language and Biology were analysed for 157 science students in four selected Senior High Schools in the Central and Western Regions. The Pearson Product Moment Correlation Analysis of the Statistical Package for Social Sciences (SPSS) was used to assess the degree of correlation between English language proficiency and academic accomplishment in Biology. The study observed that there was a positive correlation (r = 0.379, 0.479, 0.443 and 0.345) between English language performance and academic achievement in Biology in the terminal examination scores. The WASSCE scores revealed a positive and strong correlation (r = 0.825, 0.719) between English language and Biology. Based on these findings, it was recommended that since English language is extensively used in education as a whole, science teachers should teach language across the curriculum. That is, they must lay special emphasis on contextual proficiency more than on general proficiency in the language of learning and teaching (LOLT) when the need arises.