A concept of performing femtosecond electron spectroscopy in an electron microscope with adaptive optics to handle space-charge-dominated beams is presented. Improved temporal-spectral resolutions are obtained through a combination of time and energy compression optics to disentangle the spectral information buried in temporally compressed pulses. A combined similar to 1 eV-sub-ps performance with 105 electrons in single pulses, and femtosecond core-level spectroscopy at single-shots with higher doses are demonstrated. This strategy provides several orders of magnitude improvement in sensitivity compared to the state-of-the-art ultrafast electron microscopes, representing a flexible solution for studying electronic and chemical dynamics in complex systems overcoming the collective space-charge limitations. (C) 2017 Elsevier B.V. All rights reserved.