Detectives within the Professional Standards Directorate began investigating Mills in 2016 following a report from a member of staff.
He later made inappropriate comments of a sexual nature in an open working environment within earshot of several colleagues, sparking numerous complaints.
Following this incident, 37 police officers or staff who worked alongside Mills, were asked for testimonies, and significant evidence was gathered to support criminal proceedings.
In addition to the offences Mills was convicted, there were numerous other allegations made against him that amounted to breaches of GMP’s Code of Ethics and Standards of Professional Behaviour.
Detective superintendent David Jones said: “Our investigation into DS Mills uncovered alarming circumstances, whereby he preyed on women in the workplace who were simply just trying to do their jobs.
“Mills sexually assaulted his colleagues, made inappropriate remarks of a sexual nature, and acted in a disgraceful manner. He abused his position in the force and the trust of his colleagues for his own perverse gratification.
“Mill’s actions continue to have an adverse impact on many of our staff and officers who have been offered specialist support.
“Irrespective of Mills inevitably being dismissed, given he is rightly currently serving a prison sentence as a convicted sex offender, it was important we still hold these proceedings to ensure he is not only dismissed from GMP but also placed on the barred list. Mills will never work in law enforcement again.
“It is our hope today’s outcome provided closure to those who may have been seeking it, as well as reassurance that when allegations are raised, they will be thoroughly investigated and outcomes pursued.
“The actions of Mill’s are reprehensible, and there is no place for him in policing.
“We are committed to upholding the highest professional standards, and our dedicated team investigating internal matters are working tenaciously to root out offenders like Mills, who are interfering with the safety of our workplaces and unworthy of serving the public as part of Greater Manchester Police.”