The great 2011 Tohoku earthquake with Mw 9.0 generated strong shaking and a destructive tsunami along the northeastern Japan coasts. We utilize a finite‐fault model obtained from seismic P‐wave inversion to characterize the time‐dependent fault displacements and seafloor motions. A nonhydrostatic long‐wave model describes the resulting tsunami for investigation of the generation mechanism in terms of the rupture process and the ocean wave dynamics over the continental margin. The computed near‐field tsunami, which evolves from two dominant wave components generated by seafloor uplift near the epicenter and trench, is consistent with the recorded water‐level data around the source. Spectral analysis of the computed ocean surface elevation reveals energetic, standing edge waves with periods 32–115 min along the continental margin from Chiba to Hokkaido. While superposition of the two dominant wave components exacerbates the impact along the coasts fronting the rupture, constructive interference of standing edge waves accounts for the belated arrivals of the largest waves on the adjacent coasts and persistent wave activities in the aftermath.