This study investigates the transformative potential of Artificial Intelligence (AI) in teacher professional development (PD), concentrating on its effect on self-efficacy and instructional practices. A mixed-methods approach was used, which consisted of 60 English language teachers from Safir Language Academy. Quantitative data from pre- and post-intervention surveys, together with qualitative interviews, were analyzed to measure the effectiveness of AI-based PD programs. Results indicate significant enhancement in teachers’ self-efficacy (mean score increase from 3.2 to 4.1) and instructional practices (from 3.5 to 4.2), supported by statistically significant t-test results (p < 0.05). Teachers attributed these achievements to personalized learning experiences and real-time feedback presented by AI tools. Thematic analysis of interview data supported these findings while also identifying challenges like initial resistance to technology and the need for continuous technical support. The findings of the present study contribute to the body of research on AI in education by offering context-specific evidence from the TEFL field in Iran—an underexplored setting. It highlights the potential of AI-driven PD to modernize teacher training and provide continuous professional growth. Implications are discussed for educators, institutions, and policymakers seeking scalable, adaptive, and effective PD models for the digital age.