The proposal was introduced in response to a series of high-profile officer-involved deaths in recent years across the state.
The Assembly passed the bill without dissent last month and it's up for a final vote in the Senate on Tuesday. Assuming it passes there, it would then go to Gov. Scott Walker for his consideration.
Republican sponsors say they hope the investigation procedure would address concerns about fellow officers from the same department not being fair in their investigation.
Currently, smaller Wisconsin departments often rely on outside agencies to investigate officer-involved deaths. But the state's two biggest police departments, in Madison and Milwaukee, investigate their own officers.