An investigation found he was supposed to have got the permission of the chief constable before doing any external paid work.
Butt would have been sacked had he had not already left the force, the Independent Office for Police Conduct (IOPC) said.
A file was passed to the Crown Prosecution Service but it decided not to take the case any further.
Steve Noonan, IOPC director of operations, said: “Former inspector Butt has shown a complete disregard for the rules and acted dishonestly for his own personal gain.
“In doing so, he let down his colleagues and risked seriously undermining public confidence.”
Detective Superintendent Steve Keeley, of Greater Manchester Police’s Anti-Corruption Unit, said: “It is clear that the actions of Tariq Butt demonstrated a complete disregard for the values of honesty and trust that we and the public rightly expect of our officers.
“He blatantly breached these values for his own personal gain and left the panel no option but to dismiss him from the force. If we cannot trust his actions then we certainly cannot expect the public to do so either.”
