We study ground-and excited-state properties of all sd-shell nuclei with neutron and proton numbers 8 N, Z 20, based on a set of low-resolution two-and three-nucleon interactions that predict realistic saturation properties of nuclear matter. We focus on estimating the theoretical uncertainties due to variation of the resolution scale, the low-energy couplings, as well as from the many-body method. The experimental two-neutron and two-proton separation energies are reasonably well reproduced, with an uncertainty range of ∼ 5 MeV. The first excited 2 + energies also show overall agreement, with a more narrow uncertainty range of ∼ 500 keV. In most cases, this range is dominated by the uncertainties in the Hamiltonian. Introduction. Recent advances in nuclear theory have established the importance of three-nucleon (3N) forces in understanding the structure of medium-mass nuclei, for the evolution to the neutron and proton driplines [1][2][3][4][5] and the formation of shell structure [6][7][8][9][10][11][12][13]. Threenucleon forces are also key for realistic saturation properties of nuclear matter [14][15][16][17][18], which in turn are obtained from global analyses of all nuclei. To date, ab initio studies of medium-mass nuclei have largely focused on closedshell nuclei or isotopic chains, generally in the vicinity of semi-magic nuclei, and no comprehensive study exists to explore nuclear forces over a full range of the nuclear chart, such as the sd shell.An additional challenge is the quantification of theoretical uncertainties [19]. Calculations in oxygen and calcium isotopes based on nuclear forces derived from chiral effective field theory (EFT) [20,21] suggest that the uncertainties from the many-body methods are well controlled [4,5,11,13,22]. Therefore, uncertainties in the input Hamiltonian, such as truncations in the chiral EFT expansion or uncertainties in the low-energy couplings, likely remain the dominant source of uncertainty. Note that recently, first studies of the statistical uncertainties from numerically optimized chiral forces [23,24] and to quantify correlations between chiral EFT couplings [25,26] have been performed.In this work we investigate all sd-shell nuclei based on chiral two-nucleon (NN) and 3N interactions with realistic saturation properties. We derive microscopic valence-space Hamiltonians, which we diagonalize to obtain ground-state energies, two-neutron and two-proton separation energies, and first excited 2