He grew up in Tonga and, as a young man, joined a youth group at his parish in Kolofo'ou near the capital Nuku'alofa on the main island of Tongatapu.

He spent three years studying religious education at Loyola University, Baltimore, Maryland, graduating in 2000.

He participated in the Third Extraordinary General Assembly of the Synod of Bishops on the Pastoral Challenges of the Family in the Context of Evangelization held on October 5–19, 2014.

[3] On 14 February 2015, Pope Francis appointed Mafi a cardinal[7] with the title of Cardinal-Priest of Santa Paola Romana.

On 13 April 2015, he was appointed a member of the Congregation for the Evangelization of Peoples and of the Pontifical Council Cor Unum for Human and Christian Development.