He attended Catholic schools at Baucau and Ossu and then entered the minor seminary in Dare outside Dili, graduating in 1968.

After Monsignor Martinho da Costa Lopes was removed as apostolic administrator in 1983, his position remained vacant until Belo was appointed titular bishop of Lorium and apostolic administrator of the Diocese of Dili, the senior official of the Catholic Church in East Timor, on 21 March 1988.

[8] Belo continued on Lopes' path and after five months of taking office he preached a sermon that denounced the Kraras massacre of 1983 and condemned the many Indonesian arrests.

He further antagonized Indonesian authorities when he gave sanctuary in his own home to youths escaping the Santa Cruz massacre in 1991 and endeavoured to expose how many were killed.

[9][a] Belo capitalised upon this honour by meeting with a variety of world leaders, including US President Bill Clinton and Nelson Mandela of South Africa.

He and Bishop Basílio do Nascimento, the administrator of another diocese in East Timor, met privately with the pope on 28 October 2002.

He told an interviewer that he had left Díli because the new political situation required new leadership that could undertake the work of reconciliation without the associations he had with earlier battles.

He said he had chosen Mozambique because he did not think he could learn another language and that he had consulted his Salesian superior and Cardinal Crescenzio Sepe, who headed the Curia department responsible for missionary territory.

[19] On 28 September 2022, De Groene Amsterdammer, a Dutch magazine, reported that two men alleged Belo sexually abused them and others as children in East Timor.