Ms Devlin had said that police failed to properly investigate threatening messages against her or provide protection.
Her solicitors, KRW Law, welcomed that the Police Ombudsman agreed there were “flawed investigative failings” from the PSNI.
The firm said Ms Devlin was subjected to terrible social media abuse including well publicised threats aimed at her young child.
At first she had engaged with the PSNI “in good faith” to have the perpetrator investigated and prosecuted.
KRW Law said the perpetrator was not properly investigated despite “significant evidence” to identify and locate him.
The statement added that the PSNI failed Ms Devlin in two key respects, firstly in failing to issue arrest warrants outside the jurisdiction.
Secondly, they said the failings were compounded by the absence of any senior PSNI personnel to over see a serious investigation and complaint.
Kevin Winters, Solicitor and Senior Partner, KRW said: “KRW have to ask why such selective incompetence was allowed to facilitate the suspect in evading prosecution.
"It is both deeply unsettling that a well-known journalist should be treated in this way by the PSNI and regrettably, on a wider level, it undermines confidence in policing in Northern Ireland.
"We look forward to PSNI Professional Standards Department implementing the OPONI recommendations on the actions that now need to be taken to prevent similar reoccurrences.”
The decision was also welcomed by Patrick Corrigan, Northern Ireland Programme Director Amnesty International.
“The threats sent to Patricia Devlin were totally abhorrent and are part of a wider climate of intimidation of journalists in Northern Ireland,” he said.
"It is the responsibility of the media to shine a light into the dark corners of our society. It is the police’s responsibility to uphold their right to do so and to ensure there is no impunity for those who threaten press freedom.
"The failure of the PSNI to properly investigate this case is totally unacceptable. We hope that the outcome of the OPONI investigation will concentrate minds within the PSNI in responding to further threats to journalists in Northern Ireland.”