Purpose: Daily mood can be influenced by a range of experiences. Identifying everyday life experiences that make autistic adults happy and unhappy holds potential to foster positive mood and tackle mental health problems amongst this group. Methods: A total of 293 autistic adults between the ages of 18 to 35 years old (mean age of 26.51 years old (SD = 4.62); 43.3% female gender, 4.8% nonbinary) provided open-text responses regarding everyday sources of happiness and unhappiness. Using an iterative process of inductive coding, 14 happy themes and 22 unhappy themes of mood-changing life experiences were identified based on self-report qualitative data. Results: Common themes across the happy and unhappy domain involved social partners, social interactions, and engagement in recreational and employment activities, with additional distinct themes specific to happy or unhappy mood. Top themes identified in the happy domain emphasizes encouraging quality relationships and positive interactions with others and cultivating supportive work/societal environments to build a sense of achievement and value. Meanwhile, emotional tolls accompanied negative relationships and interactions, underscoring the necessity to provide autistic adults with conflict resolution and coping skills to increase feelings of happiness. Conclusion: Overall, the wide range of sources of happy and unhappy everyday experiences highlights the importance of considering personal preferences in engagement with others and activities in treatment.