Energy conservation in public buildings is an important means towards reducing CO2 emissions worldwide and tackling climate change. In this context, employee behaviour has been recognised as a highly impactful factor that needs to be studied more thoroughly. In this study, we propose and investigate a behavioural model that can be utilised in energy-saving interventions in the workplace. Employing a questionnaire (N = 119 employees in three workplaces in EU countries), we identified two types of energy consumption behaviour at work: personal and collective actions. We further investigated the effect of six factors on employee willingness, as well as self-reported energy-saving habits and behaviour. We found that an employee’s profile (i.e., i. personal energy-saving norms, ii. emotional exhaustion/burnout, iii. collective energy-saving responsibility and efficacy, iv. awareness of energy wastage and knowledge of solution, v. personal comfort/comfort levels, vi. age, vii. gender, and viii. having children) determines energy-saving habits and behaviour, as well as affects willingness to alter it and to conserve energy at work. Employee willingness in turn directly affects energy-saving habits and behaviour at work. The proposed behavioural model can provide guidance towards applying energy conservation initiatives in the workplace. Behavioural interventions should accordingly primarily focus on improving personal energy-saving norms at work and be designed to be easy to follow and not overly demanding, time consuming, or pressuring. Moreover, to motivate collective energy-saving behaviours, interventions should focus on increasing employees’ collective energy-saving responsibility and efficacy, while respecting their personal comfort/comfort levels and their emotional exhaustion/burnout levels. Practical advice towards specific types of interventions is provided accordingly.