This corpus-based research analysed three lexical features (lexical diversity, lexical sophistication, and cohesion) in English argumentative writing and examined the potential differences in lexical performance (1) between native and nonnative English writers and (2) across all writers from various language backgrounds. The findings revealed that nonnative English writers demonstrated significantly lower performance in lexical sophistication than did native English writers. Significant differences in all three lexical aspects exist between writers from different language backgrounds. Pedagogical implications for vocabulary instruction in academic writing for nonnative writers include emphasizing the mastery of academic, low-frequency, and discipline-specific vocabulary. Additionally, improving nonnative writers’ vocabulary size and lexical diversity is essential for building deeper level cohesion in writing. The results suggest unique writing characteristics of different nonnative writers and their varied learner needs should be acknowledged. Thus, targeted instruction is essential to provide effective enhancement to nonnative English writers’ lexical performance in academic writing.