A senior policing source has warned of political interference in the work of the Chief Constable – claiming the PSNI's top officer faces "a battle a day".
Matt Baggott yesterday confirmed he will step down from the role. He is under contract until September but may leave Northern Ireland before then.
Mr Baggott, who has been a police officer for 37 years, took up the job in August 2009.
The Belfast Telegraph has learned the favourite to replace him is current PSNI Assistant Chief Constable George Hamilton, who returned to the PSNI after a period with Strathclyde Police.
This newspaper understands his accession to the top policing post – which carries a salary of £190k a year – has the backing of both the DUP and Sinn Fein.
The Policing Board, which will oversee the appointment and that of the new Deputy Chief Constable, will meet to discuss the candidates next month.
Last night, a senior police source said whoever is chosen to replace 55-year-old Mr Baggott must be prepared for "a siege" as the head of the most scrutinised force in the world.
In regard to the Policing Board, the source said: "They have made it [the Chief Constable post] such an unpleasant role.
"It sounds to me like a battle a day – a siege."
While Mr Baggott's contract is due to run until September, it is understood the Policing Board may ask him to vacate the post before the parading season.
Mr Baggott's tenure as Chief Constable has been dogged by political rows and stinging criticism from both the unionist and nationalist communities.
There were also claims that members of the Policing Board recently expressed a lack of confidence in Mr Baggott.
He prepares to leave the role amid the ongoing severe threat posed by dissident republican terrorists.
Mr Baggott yesterday said: "It has been a real privilege to lead the PSNI through the immense changes of the past few years. I am deeply proud of the courage and commitment of my colleagues and the enormous progress they have made on behalf of everyone.
"In my remaining months as chief my priorities will be to ensure the PSNI has the resources to deal effectively with the many challenges ahead and that our very personal, professional and protective service goes from strength to strength."
The experienced officer spent 20 years with the Metropolitan Police and headed the team assisting the Stephen Lawrence public inquiry.
In December 2002 he became Chief Constable of Leicestershire Constabulary.
He could have applied to renew his contract with the PSNI for a further two years.
Mr Baggott's announcement came weeks after Deputy Chief Constable Judith Gillespie said she planned to retire.
Despite public fallouts, tributes were paid to Mr Baggott from across the political divide yesterday.
He was responsible for the successful policing of the Olympic torch relay, the World Police and Fire Games and the G8 summit of world leaders at Lough Erne in Co Fermanagh.
Northern Ireland Secretary Theresa Villiers (below) said: "I would like to offer sincere gratitude to the chief constable for the commitment he has demonstrated in delivering effective community policing across Northern Ireland and tackling the threat from terrorism.
"He has made an outstanding contribution to keeping the people of Northern Ireland safe."