28-year-old Jermaine Baker was shot dead in 2015 during a Metropolitan Police operation to prevent an attempted prison breakout.
Two years later prosecutors decided that the firearms officer who killed him, known as W80, would not face criminal charges.
But after their own investigation, the police watchdog, the IOPC, ruled that he should be subject to a misconduct proceeding.
That decision – which has been through various stages of appeal and counter-appeal – was today confirmed by a landmark ruling at the Supreme Court.