Born in Mohaka in the Hawke's Bay, Wainohu was a clergyman when he was appointed the chaplain to the Māori contingent that was raised for service overseas in the early stages of the First World War.

Educated at Te Aute College, he initially favoured traditional Māori beliefs such as Pai Mārire but in his later school years became a Christian.

[1] On the outbreak of the First World War, Māori were encouraged to enlist in the New Zealand Expeditionary Force (NZEF) to serve in a contingent based on ethnic lines.

[6] They were involved in the Battle of Sari Bair the following month; leading a prayer before the fighting, Wainohu urged the men to do their duty and to bear in mind their families back in New Zealand.

[7] During the battle itself, he assisted the contingent's medical officer, Major Peter Buck, and stretcher bearers in recovering the wounded and treating them.

[9] Both Wainohu and Buck had endeavoured to convince the commander of the NZEF, Lieutenant General Alexander Godley, to maintain the cohesiveness of the unit but to no avail.

At a welcoming ceremony at the Auckland Domain for the battalion before it was dismissed on 6 April 1919, Wainohu spoke to a crowd of thousands on behalf of its soldiers.

[18] Returning to civilian life, Wainohu went back to Hawke's Bay and became involved in veteran's affairs in the Wairoa Māori District.

[1][19] A memorial to Wainohu, in the form of a statue showing him in his military uniform, was unveiled by Peter Buck in Wairoa in front of 1,000 people on 16 January 1924.