 McKenna ordained bishop on 10 October 1909.During his term as Bishop he had to contend with political strife and enormous political change, most especially the effects of the Partition of Ireland which also brought political partition to his diocese.He was a strong supporter of the Irish language and culture and did not hide from aligning himself with Nationalist and Republican leaders such as Eoin O'Duffy, on one occasion giving O'Duffy a glowing reference for a post with Monaghan County Council.