This study assesses the impact of ChatGPT, an AI conversational agent, on English writing proficiency and critical thinking among freshmen at Ho Chi Minh City University of Industry and Trade. Through qualitative and quantitative methodologies, including semi-structured interviews, classroom observations, and analysis of writing samples, improvements in grammar, vocabulary, coherence, and argumentation depth were documented. While findings demonstrate significant enhancements in writing skills and stimulated critical thinking, challenges such as potential over-reliance on AI tools were also recognized. The study proposes recommendations for integrating AI in language education, emphasizing the need for balanced and critical engagement with technology.