Working memory (WM) maintains information during a delay period by internally generated neuronal activity. Here we report the dynamic organization of global cell-assembly activity that encodes WM information via cross-regional sequential spiking. Multiple Neuropixels-probe single-neuron recordings were made from over 60 brain regions in head-fixed mice performing an olfactory WM task. We found that neurons encoded WM during the delay period predominantly by transient activity that formed cross-region sequential waves, with the proportions of these neurons progressively reduced from olfactory to associative and motor regions. Spike correlogram revealed strong directional coupling of neurons coding the same memory within tens of milliseconds, especially for activity waves from olfactory to associative/motor regions. Cross-region loops were linked through functionally-coupled spikes of same memory-encoding neurons from distinct brain regions, and formed efficient graphical networks. Applying rules to reproduce experimentally observed sequential waves in artificial neural network reduced the epoch needed to convergence in the training of a WM task. Thus, structurally and functionally organized global cell-assembly dynamics mediate WM maintenance.