John Keenan is a fictional character from the British police drama HolbyBlue, portrayed by actor Cal MacAninch.

John is a detective inspector in the Criminal Investigation Department (CID) of Holby South police station.

MacAninch was involved in a long casting process for the role, but liked playing a police officer as his brothers are policemen.

The character is billed as "fearless" and "straight-talking" with a dedication to his job that damages his marriage to Kate Keenan (Zöe Lucker).

MacAninch was initially unaware that the show was a spin-off of medical drama Holby City and stated that if he had known, he might have thought twice about auditioning.

[1] John is married to station reception officer Kate Keenan, portrayed by Zöe Lucker, but his devotion to his job has estranged their marriage.

[4] The character's backstory is explored in series two with the introduction of his father, John Keenan Sr., portrayed by Kenneth Colley.

[4] The actor enjoyed working with Colley and praised his performance, commenting, "Ken doesn't look like a bully, but he manages to make him so playfully malevolent it was frightening.

John's old senior officer Detective Chief Inspector Harry Hutchinson was revealed to be a traitor feeding Stenga information about witnesses due to be giving evidence at a court trial against him, when John found out his respected mentor was corrupt he alerted the Directorate of Professional Standards (DPS) and arrested Harry resulting in his expulsion from the service, disgrace, and a prison sentence.

In the first episode of Holby Blue when John found out his wife Kate Keenan, was seeing another man after their initial divorce, he became distracted from work, at one point even organising unofficially that he would be pulled over by the uniformed branch and fined.