The LHC and ATLAS will undergo an ambitious upgrade program in preparation of the HL-LHC, referred to as phase II, to be able to deliver three times the current instantaneous luminosity. This unprecedented data-sample will allow us to perform state-of-the-art measurements at the energy frontier and will be our legacy of results in unexplored phase-space. To benefit fully from such a rich data-sample, it is crucial to upgrade the ATLAS detector to cope with the challenging experimental conditions including high levels of radiation and pile-up events. A powerful new way to mitigate the effects of pile-up is to use high-precision timing information to distinguish between collisions occurring close in space but well-separated in time. A High-Granularity Timing Detector (HGTD), based on low gain avalanche detector technology (LGAD) will significantly improve the performance in the forward region. In this talk, I will discuss the technical challenges of such a new detector, in particular the LGAD sensors and how 30 ps per track can be achieved as well as the expected performance throughout the full lifetime of the HL-LHC and roadmap towards construction.