The study explored the adoption of ChatGPT in argumentative writing among students using the Unified Theory of Acceptance and Use of Technology model as a framework. A mixed methods study was employed, and data were collected from surveys, interviews and document analysis (essays). The study revealed that participants' acceptance of ChatGPT is linked to performance expectancy, effort expectancy, facilitation conditions, social influence, self-efficacy, and habit. However, establishing habitual use is still in its initial phases, and social influences are not the primary drivers behind students' adoption of the tool. Participants reported improved organization, expanded vocabulary, and valuable writing prompts, enhancing their learning experience in argumentative writing. Participants intended to continue using ChatGPT for essay writing, acknowledging its significant contribution to argumentative writing.