He began to write poetry at an early age, chiefly, though not entirely, devoting himself to the sonnet. He took French lessons under António Feliciano de Castilho, a leading figure of the Portuguese Romantic movement, who resided in Ponta Delgada at the time. Antero was seven when he enrolled in Liçeu Açoriano (a private school), where he received English lessons from a Mr. Rendall, a renowned prospector on the island. In August 1852, he moved with his mother to the Portuguese capital, where he studied at Colégio do Pórtico, whose headmaster was his old tutor Castilho. But the institution closed its doors, and Antero returned to Ponta Delgada in 1853. On writing to his old headmaster, he would say:

"Your excellency once put-up with me at your Colégio do Pórtico when I was still ten years old, and I confess that I owe you much for your great patience, for the little French that I have known until this day."

Throughout the latter part of his life Quental would dedicate his studies to poetry, politics and philosophy. By 1855, at the age of 16, he had returned to Lisbon, then to Coimbra where he graduated from the Colégio de São Bento in 1857.

In the fall of 1856 he enrolled at the University of Coimbra, where he studied Law, manifesting his first socialist ideals.

The important fact in my life during those years, and probably the most decisive one, was the sort of intellectual and moral revolution that took place within myself, as I left a poor child, pulled away from an almost patriarchal living of a remote province immersed in its placid historical slumber, towards the middle of the irrespective intellectual agitation of a urban center, where the newly found currents of the modern spirit would come more or less to repercute. As all my Catholic and traditional upbringing swept away instantly, I fell into a state of doubt and uncertainty, as ever the more pungent as I, a naturally religious spirit, had been born to believe placidly and obey without effort to an unknown rule. I found myself without direction, a terrible state of mind, shared more or less by all those of my generation, the first one in Portugal to ever leave the old road of tradition with decision and awareness. If to this I add a burning imagination, with which Nature had blessed me in excess, the awakening of the loving passions known to early manhood, turbulence and petulance, the enthusiasms and discouragements of a meridional temperament, a lot of good faith and good will but a severe lack of patience and method, and the portrait of my qualities and defects with which I, at 18 years old, penetrated in the vast world of thought and poetry, shall be drawn.

He soon distinguished himself for his oral and written talents, as well as turbulent and eccentric nature. While in Coimbra, he founded the Sociedade do Raio, which pretended to promote literature to the masses, but which launched blasphemous challenges to religion.

In 1861, he published his first sonnets. Four years later, he published Odes Modernas, influenced by the Socialist Experimentalism of Proudhon, who championed an intellectual revolution. During that year a conflict (which would later be known as Questão Coimbrã) would develop between the traditionalist poets, championed by António Feliciano de Castilho (at that time the chief living poet of the elder generation), and a group of students (which included Antero Quintal, Teófilo Braga, Viera de Castro, Ramalho Ortigão, Guerra Junqueiro, Eça de Queiros, Oliveira Martins, Jaime Batalha Reis and Guilherme de Azevedo, among others). The contact with the nation's cultural and literary elite, the liberal and progressives in academia, did not identify with the aesthetic formalism in the literature of the day. Accusing this modernist group of poetic exhibitionism, obscurity, and generally a lack of good sense and taste, Castilho attacked the modernist poets for instigating the intellectual revolution. In response, Antero published Bom Senso e Bom Gosto, A Dignidade das Letras and Literaturas Oficiais in which he defended their independence, pointing to the mission of poets in an era of great transformation, the necessity of being the messengers of the great ideological questions of the day, and included the ridiculousness and insignificance of Castilho's style of poetry under the circumstances. This gave rise to the 1865 controversy known as the "Coimbra Question", and his groups reference as the 70s Generation which opposed the ultra - romantic group of António Feliciano de Castilho.

He then traveled, engaged in political and socialist agitation, and found his way through a series of disappointments to the mild pessimism. Strangely, it animated his latest poetry. In 1866 he went to live in Lisbon, experimented with proletarianism, worked as a typographer (at the National Press), a job that he also continued in Paris (where he went to support French workers), between January and February 1867.

He briefly went to the United States, but returned to Lisbon in 1868, where he formed Cenáculo, along with Eça de Queirós, Guerra Junqueiro and Ramalho Ortigão; a intellectual group of anarchists against many of the political, social and intellectual conventions of the day.

Paradoxically, he was a founder of the Partido Socialista Português (Portuguese Socialist Party). In 1869, he founded the newspaper, A República - Jornal da Democracia Portuguesa with Oliveira Martins, and in 1872, along with José Fontana, he began to edit the magazine O Pensamento Social. In the year of the Paris Commune (1871) he organized the famous Conferências do Casino (English: Casino Conferences), which marked the beginning of the spread of Socialist and Anarchist ideas in Portugal, distinguishing himself as a crusader for republican ideals.

In 1873, he inherited a sizable amount of money, which allowed him to live reasonably. Owing to tuberculosis in the following year, he rested, but returned to re-edit his Odes Modernas. He moved to Oporto in 1879, and in 1886 he published his best poetic work, Sonetos Completos, which included many passages considered autobiographical and symbolistic.

In 1880, he adopted the two daughters of his friend, Germano Meireles, who died in 1877. During a trip to Paris he became seriously ill, and in September 1881, under counsel from his medic, he began residing in Vila do Conde, where he remained until May 1891 (with a few intervals in the Azores and Lisbon). His time in Vila do Conde was considered by the author the best of his life. To Carolina Michaelis de Vasconcelos, a friend, he wrote of his need to end his poetry and begin a philosophical phase in his writing, to develop and synthesize his philosophy, adding:

Here the beaches are plentiful and beautiful, and through them I travel or stretch in the sun with a voluptuousness that only the poets and the lizards that love the sun...

In 1886, his Sonetos Completos, collected and prefaced by Oliveira Martins, were published. Between March and October 1887 he returned to the Azores, then back to Vila do Conde. The Spaniard, Miguel de Unamuno, considered them "one of the greatest examples of universal poetry, which will live as long as people have memories."

In reaction to the English Ultimatum, on 11 January 1890, he agreed to preside over the minor Liga Patriótica do Norte (English: Northern Patriotic League), although his involvement was ephemeral. When he eventually returned to Lisbon, he stayed at the home of his sister, Ana de Quental.

Throughout his life Antero had oscillated between pessimism and depression; afflicted with what have been Bipolar Disorder, at the time of his last trip to Lisbon he was in a state of permanent depression, which was also accentuated by spinal disease. After one month in Lisbon, around June 1891, he returned once more to Ponta Delgada, eventually committing suicide on 11 September 1891, with two gunshots through the mouth, taken on the bunk of a local garden park: "Of all things, the worst is having been born", he wrote in a poem.

Antero stands at the head of modern Portuguese poetry after João de Deus. His principal defect is monotony: his own self is his solitary theme, and he seldom attempts any other form of composition than the sonnet. On the other hand, few poets who have chiefly devoted themselves to this form have produced so large a proportion of really exquisite work. The comparatively few pieces in which he either forgets his doubts and inward conflicts, or succeeds in giving them an objective form, are among the most beautiful in any literature. The purely introspective sonnets are less attractive, but equally finely wrought, interesting as psychological studies, and impressive for their sincerity. His mental attitude is well described by himself as the effect of Germanism on the unprepared mind of a Southerner. He had learned much, and half learned more, which he was unable to assimilate, and his mind became a chaos of conflicting ideas, settling down into a condition of gloomy negation, save for the one conviction of the vanity of existence, which ultimately destroyed him. A healthy participation in public affairs might have saved him, but he seemed incapable of entering upon any course that did not lead to delusion and disappointment.

As a prose writer Quental displayed high talents, though he wrote little. His most important prose is the Considerações sobre a philosophia da historia literaria Portugueza, but he earned fame by his pamphlets on the Coimbra question, Bom senso e bom gosto, a letter to Castilho, and A dignidade das lettras e litteraturas officiaes.

His friend Oliveira Martins edited the Sonnets (Oporto, 1886), supplying an introductory essay; and an interesting collection of studies on the poet by the leading Portuguese writers appeared in a volume entitled Anthero de Quental. In Memoriam (Oporto, 1896). The sonnets have been translated into many languages; into English by Edgar Prestage (Anthero de Quental, Sixty-four Sonnets, London, 1894), together with a striking autobiographical letter addressed by Quental to his German translator, Dr. Storck.