Constructing a large, international research infrastructure is a complex task, especially when a large fraction of the equipment is delivered as in-kind contributions. A mature project management approach is essential to lead the planning and construction to deliver scientifically and technically. The purpose of this paper is to present how the ESS accelerator project is managed in terms of planning and scheduling from the design phase until commissioning, keeping time, budgets and resources constraints, as well as creating and maintaining a strong and trust-based partnership with the external contributors