Matt Baggott is to retire from his role as PSNI Chief Constable.
Mr Baggott has led the PSNI since 2009 after succeeding Hugh Orde and has been involved in policing for 37 years.
He has faced an upsurge in violence from dissident republicans opposed to the peace process, loyalists protesting against flag restrictions and contentious marches.
Mr Baggott's contract ends in September and he said it had been a privilege to lead the PSNI through the changes of the past few years.
He said: "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."
Northern Ireland Secretary Theresa Villiers said Mr Baggott made an "outstanding contribution to keeping the people of Northern Ireland safe and secure."
Police Federation for Northern Ireland chairman Terry Spence described Mr Baggott as "a chief officer of the utmost integrity who has displayed loyalty to his colleagues in the most challenging policing environment in the western world".
SDLP Policing Board member Dolores Kelly said Mr Baggott's focus on community policing and his track record of making the most of limited resources made him the best person to take the helm of the PSNI in a turbulent time.
However, she said it would be wrong to suggest that his tenure was not without disappointment and said the "slow, at times timid", response to street protests dealt "significant damage" to community confidence in the police.
Ms Kelly said the PSNI continues to face challenges and having a robust senior team in place is imperative.