The process of exploring and committing to one’s identity for the sake of a future-oriented goal is important for young adults’ psychosocial functioning. Whereas the relationship between identity process and psychosocial functioning has been examined in long-term longitudinal studies, the short-term relationship between the two at the daily level has not been clarified. This study developed a measure of daily-level identity process and examined their relationship with daily positive and negative emotions, using a five-day daily-diary method. The participants included 721 Japanese young adults aged 18–30 years (54.4% female, Mage = 26.05 years). Results indicated the measure’s three-factor structure, including commitment, active exploration, and ruminative exploration. Commitment related positively to life satisfaction and happiness, and negatively related to depression. Active exploration and ruminative exploration indicated negative associations with life satisfaction and happiness, and positive association depression. Latent profile analysis extracted five theoretically meaningful identity profiles at the daily level: foreclosure, moratorium, troubled diffusion, searching moratorium, and carefree diffusion. Logistic regression analyses indicated that troubled diffusion and moratorium, and foreclosure profiles showed lower and higher levels of life satisfaction and happiness, respectively. These results provided evidence of a strong link between young adult’s identity processes, profiles, and positive and negative emotions at the everyday level. Implications and suggestions for future research are discussed.