Subjective wellbeing (SWB) encompasses an individual’s cognitive and affective evaluations of his or her life and includes life satisfaction, positive affect, and negative affect (NA). SWB and diet quality are both associated with longevity and health outcomes, yet research uniting the topics has been disjointed. In this study, subjective vitality (SV) was explored as a mechanism through which diet quality and SWB may be related. Seventy-three undergraduate psychology students completed an online survey with the Satisfaction with Life Scale, the Positive and Negative Affect Schedule, the Subjective Vitality Scale, the Estimated Daily Intake Scale—Sugar, and a Dietary Screener Questionnaire. Indirect effects of diet quality (plant-based/natural (PBN) diet intake, animal-based/processed (ABP) diet intake, daily sugar intake) on SWB through SV were tested using bootstrapping according to Hayes (in: Weber (ed) Methodology in the social sciences, Guilford Press, New York, 2013). Results showed significant indirect effects between each dietary predictor (PBN, ABP, daily sugar) and SWB components through SV. Subjective vitality was significantly positively associated with PBN and SWB, and significantly negatively associated with daily intake of added sugar. Additionally, PBN positively predicted SV, which in turn positively predicted SWB. Significant positive direct and indirect effects were also found between ABP and NA through SV. Implications for healthy diet interventions to improve well-being are discussed.