Justice Isaac Lenaola subsequently directed the National Police Service Commission to conduct a repeat exercise.
He ordered the commission not to issue any appointment letters from the previous result, which he ruled was marred by massive graft and nepotism allegations.
The judge said the commission violated the Constitution by delegating the duty to a non-entity at the county level.
He ruled that the commission not only failed itself but the country, Constitution, recruits and the public as a whole.
The National Police Service Commission had earlier nullified the recruitment exercise in some centres, whose affected candidates filed cases in court challenging the decision.
The case leading to the entire nullification was filed by the Independent Policing Oversight Authority chairman Macharia Njeru.