Walking Works Wonders (WWW) is a workplace intervention designed to increase physical activity and reduce sedentary behaviour. WWW involves tailoring health information according to employees’ readiness for change. The approach recognises that when attempting to motivate behaviour change, success is greater when interventions align with recipients’ attitudes and beliefs. The impact of the tailored approach was investigated by comparing tailored interventions with standard conditions and control groups in a 24-month longitudinal study in 10 worksites across the UK. Employees who received either a standard or tailored intervention demonstrated significantly higher self-reported work ability and improved organizational commitment, job motivation, job satisfaction, and a reduction in intention to quit the organization. The tailored interventions significantly reduced BMI and waist circumference compared to standard and control conditions. Workplace health interventions designed to increase physical activity and reduce sedentary behaviour are likely to be more effective where the information is tailored to employees’ readiness to change.