Long hours and shift work have been associated with cardiometabolic disease risk. Despite diet being an established modifiable risk factor, few studies have examined how dietary behaviours vary in relation to working hours. The aim of this thesis was to investigate the relationship between working hours and diet quality with markers of cardiometabolic health. Cross-sectional analyses were conducted using data from The Airwave Health Monitoring Study - a British police occupational cohort (n=5,849). Number of weekly working hours was determined from questionnaire data. The Dietary Approaches to Stop Hypertension score was calculated using 7-day diet data to measure diet quality. Markers of cardiometabolic health included: adiposity (body mass index, waist circumference and body fat), blood pressure, cholesterol, HbA1c and C-reactive protein. Sub-group analyses were conducted in participants with available shift work data (based on police radio records) (n=2,323). As part of this thesis a revised food diary and shift work questionnaire were developed and piloted for use in future studies. Male employees (n=3,332) working >49hrs per week (vs. 35-40hrs) were more likely to have a dietary pattern associated with elevated cardiometabolic risk. There was a positive dose-response relationship across working hours (!35-40, 41-48, 49-54, !55hrs per week) with markers of adiposity in male employees. Diet quality did not modify this association. Based on limited shift work data: night workers (vs. day) were found to consume a higher quantity of sugar-sweetened beverages. However shift work was not associated with increased cardiometabolic risk. This thesis suggests a sex specific positive association between weekly working hours and adiposity that is independent of established risk factors. Temporal eating pattern and previous shift work data collected using the revised food diary and shift questionnaire will be important to future studies exploring the relationship between diet, work hours and health.