After the second trial he received a three-year prison sentence at London's Southwark Crown Court.
This was reduced by the 15 months he had already spent behind bars and he has been released.
Dizaei was sacked by the Metropolitan Police following internal disciplinary proceedings.
During the hearing before Lord Judge and two other judges in London, Dizaei's QC Stephen Riordan argued that his conviction was "unsafe". He submitted that the judge at the second trial made an "error of law" when he refused to admit certain "bad character" evidence relating to Mr al-Baghdadi.
The judges reserved their decision to be given at a date to be announced.