This dissertation explores the current and potential roles of AI in a complex problem-solving. Especially, the dissertation focuses on how AI can support creative design and decision-making. Chapter 2 includes a systematic literature review and a design workshop with design experts to understand when and how to use AI in the design process. Chapter 3 compares the different roles of AI in creative design problem-solving. The study compares two different roles of AI depending on its proactivity in interaction. 1) Active AI, which helps humans understand design problems with constraints through mutual collaboration; 2) Reactive AI, which helps only when humans seek it out. Chapter 4 examines how people make decisions in AI-assisted decision-making and its ethical implications. This chapter investigates how the identity of the suggestion giver (AI vs. human experts) and the accuracy of the information (correct vs. incorrect) influence decision-making behaviors. Chapter 5 provides a summary of the main findings with their design and practical implications.