Elor Azaria, 19 at the time, shot Abdul Fatah al-Sharif, 21, in the head while he was lying immobile on a road.
A military court convicted the soldier after dismissing his assertion that the Palestinian still posed a danger.
The case has divided Israeli opinion. Azaria, a sergeant, will be sentenced next Sunday, Israel's military says.
There have been rallies to support the soldier, but top military figures say his actions do not reflect the values of the Israel Defence Forces (IDF).