This study investigates the impact of AI, particularly Large Language Models (LLM) like ChatGPT, on job design and work outcomes in Professional Service Firms (PSFs). While the debate has predominantly centred on AI's potential for task automation, this research shifts focus on a comprehensive understanding of AI's determinants and their effects on job design and individual work outcomes. Through a qualitative exploratory study of consultants, we propose a conceptual framework and identify two key mechanisms: one altering job design through transformative or enabling effects and the other directly influencing work. Our findings contribute to the literature by providing a nuanced view of AI's role in job design and outcomes, also underscoring the transformative role of AI in New Ways of Working (NWW) and highlighting its implications in knowledge-intensive settings like PSFs.