Born in Villahermosa, Tolima, López Trujillo moved to Bogotá as a young boy and attended the National University of Colombia before he entered the seminary in order to become a priest.

Well known for his dislike and distrust of the radical social agenda espoused by many Latin American priests and bishops, in this capacity he led the opposition to liberation theology and succeeded in watering down or reversing many of the reforms made in that forum.

[3] Andrew Sullivan, an American pro-LGBT activist, writing in the New York magazine, has claimed that he would go with paramilitaries into rural areas and slums, and tell them which priests were involved with social work or believed in liberation theology, which often caused the paramilitaries to murder those priests or force them into hiding or exile[4] One of his major accomplishments during that period was to organize the third general conference of Latin American Bishops in 1979, in which Pope John Paul II participated.

[8] This claim was refuted by the World Health Organisation as "scientifically incorrect" in a formal statement, reflecting their position that condoms provide effective protection against HIV transmission.

He was also a strong opponent of gay marriage,[12] abortion (a stance that won him much praise and support from groups such as the Society for the Protection of Unborn Children[13]) and embryological research, warning Catholics involved in the creation of embryos as part of IVF treatment for infertility that they would be excommunicated.

"[15] A further article in The New York Times reviewing Martel's book suggests Trujillo "prowled the ranks of seminarians and young priests for men to seduce" and "routinely hired male prostitutes, sometimes beating them up after sex".