Eco was born in the city of Alessandria in the region of Piedmont (northern Italy). His father, Giulio, was an accountant before the government called upon him to serve in three wars. During World War II, Umberto and his mother, Giovanna, moved to a small village in the Piedmontese mountainside. Eco received a Salesian education, and he has made references to the order and its founder in his works and interviews. His family name is supposedly an acronym of ex caelis oblatus (Latin: a gift from the heavens), which was given to his grandfather (a foundling) by a city official.

His father was the son of a family with thirteen children, and urged Umberto to become a lawyer, but he entered the University of Turin in order to take up medieval philosophy and literature, writing his thesis on Thomas Aquinas and earning his Laurea in philosophy in 1954. During this time, Eco left the Roman Catholic Church after a crisis of faith. After this, Eco worked as a cultural editor for the state broadcasting station Radiotelevisione Italiana (RAI) and also lectured at the University of Turin (1956 – 64). A group of avant-garde artists — painters, musicians, writers — whom he had befriended at RAI (Gruppo 63) became an important and influential component in Eco's future writing career. This was especially true after the publication of his first book in 1956, Il problema estetico in San Tommaso, which was an extension of his doctoral thesis. This also marked the beginning of his lecturing career at his alma mater.

In September 1962, he married Renate Ramge, a German art teacher with whom he has a son and a daughter. He divides his time between an apartment in Milan and a vacation house near Rimini. He has a 30,000 volume library in the former and a 20,000 volume library in the latter. In 1992 - 1993 Eco was the Norton professor at Harvard University. On May 23, 2002, Eco received an honorary Doctor of Letters from Rutgers University in New Brunswick, New Jersey. Eco is a member of the Italian skeptic organization CICAP.

In 1959, he published his second book, Sviluppo dell'estetica medievale (The Development of Medieval Aesthetics), which established Eco as a formidable thinker in medievalism and proved his literary worth to his father. After 18 months' military service in the Italian Army, he left RAI in 1959 to become the senior non-fiction editor of the Bompiani publishing house in Milan, a position he occupied until 1975. Eco's work on medieval aesthetics stressed the distinction between theory and practice. About the Middle Ages, he wrote that there was "a geometrically rational schema of what beauty ought to be, and on the other [hand] the unmediated life of art with its dialectic of forms and intentions" — the two cut off from one another as if by a pane of glass. Eco's work in literary theory has changed focus over time. Initially, he was one of the pioneers of "Reader Response".

During these years, Eco began seriously developing his ideas on the "open" text and on semiotics, penning many essays on these subjects, and in 1962 he published Opera aperta (Loose work). In it, Eco argued that literary texts are fields of meaning, rather than strings of meaning, that they are understood as open, internally dynamic and psychologically engaged fields. Literature which limits one's potential understanding to a single, unequivocal line, the closed text, remains the least rewarding, while texts that are the most active between mind and society and life (open texts) are the most lively and best — although valuation terminology is not his primary area of focus. Eco emphasizes the fact that words do not have meanings that are simply lexical, but rather, they operate in the context of utterance. So much had been said by I.A. Richards and others, but Eco draws out the implications for literature from this idea. He also extended the axis of meaning from the continually deferred meanings of words in an utterance to a play between expectation and fulfilment of meaning. Eco comes to these positions through study of language and from semiotics, rather than from psychology or historical analysis (as did theorists such as Wolfgang Iser, on the one hand, and Hans-Robert Jauss, on the other). He has also influenced popular culture studies though he did not develop a full-scale theory in this field.

Eco co-founded Versus: Quaderni di studi semiotici (known as VS in Italian academic jargon), an influential semiotic journal. VS has become an important publication platform for many scholars whose work is related to signs and signification. The journal's foundation and activities have contributed to the growing influence of semiotics as an academic field in its own right, both in Italy and in the rest of Europe. Most of the well-known European semioticians, among them Umberto Eco, A.J. Greimas, Jean-Marie Floch, Paolo Fabbri, Jacques Fontanille, Claude Zilberberg, Ugo Volli and Patrizia Violi, have published original articles in VS. Articles by younger, less famous scholars dealing with new research perspectives in semiotics also find place in almost every issue of VS.

In 1988, at the University of Bologna, Eco created an unusual program called Anthropology of the West from the perspective of non-Westerners (African and Chinese scholars), as defined by their own criteria. Eco developed this transcultural international network based on the idea of Alain Le Pichon in West Africa. The Bologna program resulted in a first conference in Guangzhou, China, in 1991 entitled "Frontiers of Knowledge." The first event was soon followed by an Itinerant Euro-Chinese seminar on "Misunderstandings in the Quest for the Universal" along the silk trade route from Canton to Beijing. The latter culminated in a book entitled The Unicorn and the Dragon, which discussed the question of the creation of knowledge in China and in Europe.

In 2000 a seminar in Timbuktu (Mali), was followed by another gathering in Bologna to reflect on the conditions of reciprocal knowledge between East and West. This in turn gave rise to a series of conferences in Brussels, Paris, and Goa, culminating in Beijing in 2007. The topics of the Beijing conference were "Order and Disorder", "New Concepts of War and Peace", "Human Rights" and "Social Justice and Harmony". Eco presented the opening lecture. Eco's interest in East/West dialogue to facilitate international communication and understanding also correlates with his related interest in the international auxiliary language Esperanto.

Eco's fiction has enjoyed a wide audience around the world, with good sales and many translations. His novels often include references to historical figures and texts and his dense, intricate plots tend to take dizzying turns.

Eco employed his education as a medievalist in his novel The Name of the Rose (1980), a historical mystery set in a 14th century monastery. Franciscan friar William of Baskerville, aided by his assistant Adso, a Benedictine novice, investigates a series of murders at a monastery that is set to host an important religious debate. Eco is particularly good at translating medieval religious controversies and heresies into modern political and economic terms so that the reader can appreciate their substance without being a theologian. The Name of the Rose was later made into a motion picture starring Sean Connery, F. Murray Abraham and Christian Slater. One notable fact about this book is that the underlying mystery of the murder is actually borrowed from the "Arabian Nights" - translated from the Arabic by Sir Richard Burton. The Name of the Rose is a creative and biographical tribute to Jorge Luis Borges, represented in the novel and the film by the blind monk and librarian Jorge of Burgos. Borges, like Jorge, lived a celibate life consecrated to his passion for books, and also went blind in later life.

Foucault's Pendulum (1988), Eco's second novel, has also sold well. In Foucault's Pendulum, three under-employed editors who work for a minor publishing house decide to amuse themselves by inventing a conspiracy theory. Their conspiracy, which they call "The Plan", is about an immense and intricate plot to take over the world by a secret order descended from the Knights Templar. As the game goes on, the three slowly become obsessed with the details of this plan. The game turns dangerous when outsiders learn of The Plan, and believe that the men have really discovered the secret to regaining the lost treasure of the Templars.

The Island of the Day Before was Eco's third novel. The book is about a man in the Renaissance marooned on a ship within sight of an island which he believes is on the other side of the international date-line. The main character is trapped by his inability to swim and instead spends the bulk of the book reminiscing on his life and the adventures that brought him to be marooned.

Baudolino, a fourth novel by Eco, was published in 2000. Baudolino is a knight who saves the Byzantine historian Niketas Choniates during the sack of Constantinople in the Fourth Crusade. Claiming to be an accomplished liar, he confides his history, from his childhood as a peasant lad endowed with a vivid imagination to his role as adopted son of Emperor Frederic Barbarossa, to his mission to visit the mythical realm of Prester John. Throughout his retelling, Baudolino brags of his ability to swindle and tell tall tales, leaving the historian (and the reader) unsure of just how much of his story was a lie.

The Mysterious Flame of Queen Loana is Eco's fifth novel and is about Iambo Bodoni, an old bookseller specialized in antiques who emerges from a coma with only memories to recover his past. In an interview during 2009 London Book Fair, Eco dismissed the rumors of The Mysterious Flame of Queen Loana being his last novel, stating that he is a "young novelist" and may write more novels in the future.

Eco's work illustrates the concept of intertextuality, or the inter-connectedness of all literary works. His novels are full of subtle, often multilingual, references to literature and history. For instance, the character William of Baskerville is a logically-minded Englishman who is a monk and a detective, and his name evokes both William of Ockham and Sherlock Holmes (by way of The Hound of the Baskervilles). Eco cites James Joyce and Jorge Luis Borges as the two modern authors who have influenced his work the most.