Engagement in personally meaningful activities is associated with greater well-being. However, most studies use cross-sectional or recall methods, and the researchers pre-determine which activities are 'meaningful.' This study examined an idiographic measure of meaningful activity participation in relation to well-being. Participants (N = 160; M age = 43.3 years; 77% female) rated the meaningfulness of 46 daily activities at baseline and reported their activities on eight random days over the next 4 weeks. Half the participants also completed measures of meaning salience and mood on the same days. All participants reported on psychological well-being at baseline and 4-week follow-up. Meaningful activity participation was positively associated with meaning salience and positive mood. Average engagement in meaningful activities over 8 days was positively associated with subjective vitality, life satisfaction, and purpose in life at follow-up. An idiographic measure of meaningful activity participation may further be understanding of the relationship between meaningful activity participation and well-being. Abbreviations: ACT - Acceptance and Commitment Therapy; LET - Life Engagement Test; MALM - Meaningful Activity and Life Meaning; MAPA - Meaningful Activities Participation Assessment; PANAS - Positive and Negative Affect Schedule; PHQ-8 - Patient Health Questionnaire-8; SDT - Self-determination Theory; SVS - Subjective Vitality Scale; SWLS - Satisfaction with Life Scale; TOMS - Thoughts of Meaning Scale