Horiana has a Bachelor of Laws and a Bachelor of Arts (majoring in Māori Resource Management) from Victoria University of Wellington and a Master of Laws from Harvard Law School.

Horiana is the Managing Director of Whāia Legal, a kaupapa Māori law firm that works predominantly for Māori clients across different areas of law.

In her legal mahi, Horiana pushes the status quo to affect change within, and outside of, the legal system to recognise the unique place of whānau, hapū and iwi within Aotearoa. Horiana is committed to social change in Aotearoa through the law and other vehicles.

Her iwi are Ngāti Porou, Ngāti Kahungunu and Rakaipaaka.