He learned photography principally from Manuel Álvarez Bravo along with influences from Francisco Monterde, Ricardo Razaetti, film director Alejandro Galindo and writer Xavier Villaurrutia .
[2][3] He began his photography career at a time when most photographers were constrained by Mexico's politics and the desire to create a unified Mexican identity, something he learned to reject under the Alvaréz Bravo.
[2][5] His early photographic work included subjects such as 15 de Septiembre Street, dancers, masks and carnivals as well as teachers’ strikes, Huichol and Cora peoples.
With a bent for social criticism, his work focused more on the negative aspects of Mexico's then-economic development and official claims of a unified Mexican identity.
[5] Lopez was also the cameraman for the short film Todos somos mexicanos, sponsored by the Instituto Nacional Indigenista and directed by José Arenas.
[5][9] His photography never focused on “hard news” even though a number of important events happened in his time such as the miners’ Hunger March in 1951 and the 1968 student movement.
[11] He rarely photographed celebrities and politicians with the notable exceptions of the inauguration of Rafael Ávila Camacho as governor of Puebla and the wedding of Anastasio Somoza in Nicaragua.
[9] Shortly before his death, he gathered a collection of about 30,000 negatives, 3,000 and three films to donate to the federal government photographic archives located in Pachuca, Hidalgo, now guarded as the Fondo Nacho López.
[16] These influences helped him to develop a kind of “modernist objectivity” and ethics for his work with magazines in strong contrast to the emphasis on the exotic and political pressures.
[1][3][10] In addition to Alvarez Bravo and Modotti, his work has also been compared to Dorothea Lange, Henri Cartier-Bresson and Edward Weston, all of which were again exoticism in Mexican photography.
[6] López’s most powerful photo essays tended to focus on the downtrodden such as prisoners, slum inhabitants, poor children, illiterates and the socioeconomically marginalized.
[8][14] This allowed him to develop the photo essay format, and was the first Mexican journalist to significantly expand the notion of being an author, writing the captions and other texts that accompanied his images.
Even when he did well known topics such as the annual pilgrimage to the Basilica of Our Lady of Guadalupe in Mexico City in December, he would focus on different things such as what the pilgrims ate and drank.
[4][6][13] This photo was the result of a woman with a very narrow waist, in reality Maty Huitron, an actress hired by López, walking in downtown Mexico City and in other settings so that Lopéz could photograph bystanders’ reactions to her.
[6][13] According to historian John Mraz, his most critical photo-essay was called “Solo los humildes van al infierno,” (Only the humble go to hell) published in Siempre!