His father, Serafim Augusto Marto, was a Fiscal Guard and his mother, Maria da Purificação Correia dos Santos, a schoolteacher.

[3] António Marto was very fond of the local parish priest, who he used to engage in conversation, and who left him with a lasting impression on how he was held in high esteem by the whole community.

At age 10, following his primary school education, António unexpectedly expressed his desire to become a priest; he initially met some resistance from his father, who even though was devoutly Catholic, had envisioned a career in military for him and was planning to send him to the Institute of the Pupils of the Army.

Captivated by the spirit of the French worker-priest movement, and because of the then-prevalent idea that industrial-class workers had become largely disaffected with the Church, António Marto and two colleagues took up labour for a year in a metalworking factory producing parts for vehicle engines.

[2] He concluded his doctoral thesis in 1978, titled Esperança Cristã e Futuro do Homem: Doutrina Escatológica do Concílio Vaticano II ("Christian Hope and the Future of Man: The Eschatological Doctrine of the Second Vatican Council").

[10] Marto learned of this as he was vesting for Mass at Leiria Cathedral: he noticed an unusual missed call from the apostolic nunciature and, worried that anything serious (like the Pope having died) had happened, he opened a voicemail with unexpected congratulations from Nuncio Rino Passigato on his appointment.

[13] On 25 March, Cardinal Marto renewed the consecration of Portugal and Spain to the Sacred Heart of Jesus and the Immaculate Heart of Mary, and added the names of twenty-four other countries (Albania, Bolivia, Colombia, Costa Rica, Cuba, Slovakia, Guatemala, Hungary, India, Mexico, Moldova, Nicaragua, Panama, Paraguay, Peru, Poland, Kenya, the Dominican Republic, Romania, Tanzania, East Timor and Zimbabwe) at the request of their respective episcopal conferences.

Having clarified that the signatories "are entitled to their opinion", he lamented that Traditionalist Catholics were "questioning the very faith of their bishops", and further remarked on the topic of Communion in the hand: "Jesus Himself said 'take and eat'.

"[11] Marto has cited the European migrant crisis as an example of how societies have become more aggressive due to a culture based on populism that thrives on "fear and insecurity": "It is with sadness that I see a resurgence in certain kinds of nationalism that divide a Europe that used to be open and showed solidarity.

[11] On 25 August 2018, Archbishop Carlo Maria Viganò, former apostolic nuncio to the United States, released an 11-page letter describing a series of warnings to the Vatican regarding sexual misconduct by Theodore McCarrick, accusing Pope Francis of failing to act on these reports and calling on him to resign.

[20] As the Portuguese Parliament tabled a vote on the decriminalisation of euthanasia in February 2020, Marto underlined his opposition, saying "no one could expect a servant of the Gospel to be against life.