The purpose of this study was to assess patterns of affect over the day in a representative sample of older people, with particular emphasis on the impact of loneliness and depression. Momentary assessments of positive and distressed affect were obtained four times over a single day from 4,258 men and women aged 52–79 years from the English Longitudinal Study of Ageing. Positive and distressed affect were only modestly correlated (r = −0.23). Positive affect was low on waking and peaked in the early evening, while distressed affect decreased progressively over the day. The diurnal variation in positive affect was greater in participants <65 years compared with older individuals. Positive affect was greater in men, married participants and in healthy individuals, while distressed affect was higher among women, unmarried and lower socioeconomic status respondents, and in those with limiting longstanding illnesses. Depressed individuals experienced lower positive affect throughout the day, while differences in distressed affect were more pronounced in the morning. Loneliness was associated with lower positive affect and greater distressed affect independently of age, sex, marital status, paid employment, socioeconomic status, health, and depression. This study demonstrates that ecological momentary assessment of affect is feasible on a large scale in older individuals, and generates information about positive affect and distress that is complementary to standard questionnaire measures. The associations with loneliness highlight the everyday distress and reduced happiness and excitement experienced by lonely older men and women, and these may contribute to enhanced risks to physical and mental health.