Cardinal Stephen Ameyu Martin Mulla, Archbishop of Juba (South Sudan), was born on 10 January 1964 in Ido, in the region of Eastern Equatoria, Sudan.

He received the Sacrament of the Order for the diocese of Torit on 21 April 1991. After pastoral work in the Sudanese capital Khartoum, he studied for a doctorate from the Pontifical Urbanian University of Rome from 1993 to 1997. His thesis is intitled Towards religious dialogue and reconciliation in Sudan.

Ameyu then taught at the seminary of Juba, capital of South Sudan, where he is also rector. Since 2013 he has also worked in the administration of the Catholic University of South Sudan.

On 3 January 2019 Pope Francis appointed him bishop of Torit, a diocese that had remained vacant for over five years following the death of Bishop Akio Johnson Mutek in 2013.

Archbishop Paulino Lukudu Loro M.C.C.I., of Juba, consecrated him a bishop on 3 March of the same year.

On 12 December 2019, Pope Francis appointed him archbishop of Juba. The inauguration took place on 22 March of the same year. On the same date he was also appointed as apostolic administrator of the diocese of Torit.

He was also apostolic administrator of the diocese of Wau from 21 September 2020 to 24 January 2021.

Created and proclaimed Cardinal by Pope Francis in the consistory of 30 September 2023, of the Title of Santa Gemma Galgani.