In the second half of 2026, after a shutdown period of two and one half years for a major upgrade of the accelerators infrastructure, the Large Hadron Collider (LHC) will enter the high-luminosity phase reaching an instantaneous luminosity of 7.5×10^34cm^−2s^−1 at the centre-of-mass energy of 14 TeV. To cope with those unprecedented luminosities and to be able to fully exploit the physics discovery potential, the ATLAS detector will be upgraded as well. A total of 3000 fb−1 of pp collision data should be collected over about ten years of high luminosity LHC running. In this document, simulated data studies on the ultimate precision attainable on the couplings measure- ments of the 125 GeV Higgs boson, the prospect on the sensitivities for Higgs boson rare decays as well as perspectives on the measurement of the Standard Model di-Higgs production, are pre- sented. Moreover, an overview of the expected sensitivities of the upgraded ATLAS detector to the discovery of several supersymmetric particles production are discussed.