The report claims that even if McCabe had been forthright about his actions, his disclosure still would have violated the FBI's media policy.
McCabe authorized an FBI official to speak with The Wall Street Journal about an article regarding the Clinton investigation.
Acting FBI director Andrew McCabe announced plans to retire in 2018.
In a separate statement Friday, Bromwich called McCabe's his firing rushed, "unprecedented, unseemly, and cruel", adding: "Separate and apart from our profound concerns about the process, we believe the OIG report utterly failed to support the decision to terminate Mr. McCabe". McCabe vigorously disputes its conclusions, and his team distributed a point-by-point rebuttal of the inspector general's allegations. "No collusion, all made up by this den of thieves and lowlifes!"
Trump's Twitter tirade against McCabe came on the heels of another attack on Comey, whose upcoming tell-all memoir has enraged the President.
The day he was sacked, Attorney General Jeff Sessions said in a statement that "the Federal Bureau of Investigation expects every employee to adhere to the highest standards of honesty, integrity, and accountability".
The report was released as advance copies of Comey's new memoir were obtained by the press. The account of the August 12 McCabe-PADAG call, and other information regarding the handling of the CF Investigation, was included in the October 30 WSJ article. He has also said he did not lie to the inspector general's office about the media disclosures.
"The rush to termination was nothing short of extraordinary", Bromwich said in an interview.
Bromwich also says President Trump interfered with the objectivity of Attorney General Jeff Sessions through the application of considerable public pressure.
The report says McCabe twice told investigators that he didn't know anything about how the information got out. "McCabe was sacked in disgrace for misconduct and lying about it".
Rep. Bob Goodlatte, R-Va., the chairman of the House Judiciary Committee, said the report makes it clear that "Sessions made the right decision" in firing McCabe. Comey accuses the president of being "untethered to truth", and describes in detail his interactions with Mr. Trump. But she also disclosed that the Clinton Foundation, the Clinton family charity, was under investigation.
McCabe contacted the NY official again on November 4 following the publication of another Wall Street Journal article that referred to the information McCabe had leaked.