The Northumbria Police and Crime Panel confirmed the appointment today and he will take up the role immediately.
Mr Keenen, Police and Crime Commissioner Dame Vera Baird’s preferred candidate, has been Acting Chief Constable since last October.
Panel chairman Coun Angela Douglas said: "It is clear that the new Chief Constable underwent a thorough, rigorous process to become Chief Constable. The panel process worked really well, with a good level of interest in the role and the panel's decision was unanimous and we are looking forward to working with the new Chief Constable and the Commissioner in making Northumbria an even safer place to live and work."
The Chief Constable said he was honoured to have been appointed.
"We have a great team of officers and staff who are making a real difference and I want to work with them to build on their successes and deliver the best policing possible for the communities we serve," he said.
"Dame Vera has set her vision out in the Police and Crime Plan, our job is to deliver that vision and I am determined to do this. Policing continues to face many challenges but the entire team in Northumbria are up for the task and I look forward to being part of this."
Commenting on the panel’s endorsement, Dame Vera said: "I am delighted that the panel has approved my decision to appoint Mr Keenen as the next Chief Constable for Northumbria.
"Mr Keenen knows the communities of Northumbria and he has many years of exceptional policing experience which will continue to pay dividends in his role as Chief Constable.
"The Chief Constable has worked hard to improve policing right across the force area – I know he will continue this drive in his new role.
"The panel clearly saw the merits and skills that Mr Keenen will bring to the role. This is a new era for our force and our new Chief Constable is proud to serve Northumbria. I have every confidence in his capabilities to lead Northumbria Police and I look forward to working with him to deliver the priorities within the Police and Crime Plan."
Mr Keenen joined Northumbria in 1985 as a police officer, became Assistant Chief Constable in 2014 and became Deputy in 2015.