After studying law in Madrid, he entered the University of Oviedo in 1870, graduated and served at the university as a professor of law and political economy, a position he held until his death. He published thousands of articles in national magazines and newspapers, through which he cultivated drama, poetry and fiction. These articles were collected in about 30 volumes, occasionally mixing articles with short stories, as in Clarín Solos (1881).
His most important novels, The Regent (2 vol., 1884-85) and His only son (1890), are among the best Spanish novels of the 19th century. Although often called naturalistic novels, none adhere to the scientific principles of naturalism or its characteristic depiction of squalor and violence. Where naturalism rejects the spiritual and the psychological in favor of behavioral observation; the novels of At they avoid the emphasis on the physiological, instead, they sensitively explore the haunted psyches of a disintegrating soul (The Regenta) and a seeker who loses his way (Her only son).
On The Regent, Alas mercilessly described the provincial society of Vetusta, an imaginary city inspired by Oviedo, Spain. The novel analyzes the decadent society of the Restoration, from the perspective of a stranger, Ana Ozores, sometimes called the Madame Bovary of Spain. Isolated by the benign neglect of her elderly husband and victimized by the closed-minded, morally conservative, and misogynistic Spanish society, she suffers a spiritual and psychological decline that resembles what At perceived as the collective evils and the degeneration of his country.
On His only child, the central character, Bonifacio Reyes, is a weak and romantic dreamer married to a spoiled, dominant and rich woman. He escapes from his painful marriage by frequenting theater and opera groups. Dissatisfied with life, he seeks a deeper meaning. The novel’s ironic title alludes to doubts about whether his only son was fathered by another while he found consolation with actresses. A somewhat enigmatic novel, His Only Son moves between scathing satire and gentle reverie.
At wrote several outstanding short novels, and is also considered the father of the modern Spanish short story. His intellectual integrity and ethical concerns appear in his extensive collections that include Pipe (1886), Doña Berta, raven, trickery (1892), The lord and the others are stories (1893), Moral tales (1896) and Socrates’ rooster (1901), all marked by their characteristic humor and sympathy for the poor, the lonely, and the oppressed.