Born in Glasgow, Thomas Campbell was the youngest son of Alexander Campbell, of the Campbells of Kirnan, Argyll. His father belonged to a Glasgow firm trading in Virginia, and lost his money in consequence of the American Revolutionary War. Campbell, who was educated at the Glasgow High School and University of Glasgow, won prizes for classics and for verse-writing. He spent the holidays as a tutor in the western Highlands. His poem Glenara and the ballad of Lord Ullin's Daughter owe their origin to a visit to Mull. In May 1797 he went to Edinburgh to attend lectures on law. He supported himself by private teaching and by writing, towards which he was helped by Dr Robert Anderson, the editor of the British Poets. Among his contemporaries in Edinburgh were Sir Walter Scott, Henry Brougham, Francis Jeffrey, Dr Thomas Brown, John Leyden and James Grahame. These early days in Edinburgh influenced such works as The Wounded Hussar, The Dirge of Wallace and the Epistle to Three Ladies.
In 1799, six months after the publication of the Lyrical Ballads of Wordsworth and Coleridge, The Pleasures of Hope was published. It is a rhetorical and didactic poem in the taste of his time, and owed much to the fact that it dealt with topics near to men's hearts, with the French Revolution, the partition of Poland and with negro slavery. Its success was instantaneous, but Campbell was deficient in energy and perseverance and did not follow it up. He went abroad in June 1800 without any very definite aim, visited Gottlieb Friedrich Klopstock at Hamburg, and made his way to Regensburg, which was taken by the French three days after his arrival. He found refuge in a Scottish monastery. Some of his best lyrics, Hohenlinden, Ye Mariners of England and The Soldier's Dream, belong to his German tour. He spent the winter in Altona, where he met an Irish exile, Anthony McCann, whose history suggested The Exile of Erin.
He had at that time the intention of writing an epic on Edinburgh to be entitled The Queen of the North. On the outbreak of war between Denmark and England he hurried home, the Battle of the Baltic being drafted soon after. At Edinburgh he was introduced to the first Lord Minto, who took him in the next year to London as occasional secretary. In June 1803 appeared a new edition of the Pleasures of Hope, to which some lyrics were added.
In 1812 he delivered a series of lectures on poetry in London at the Royal Institution; and he was urged by Sir Walter Scott to become a candidate for the chair of literature at Edinburgh University. In 1814 he went to Paris, making there the acquaintance of the elder Schlegel, of Baron Cuvier and others. His pecuniary anxieties were relieved in 1815 by a legacy of £4000. He continued to occupy himself with his Specimens of the British Poets, the design of which had been projected years before. The work was published in 1819. It contains on the whole an admirable selection with short lives of the poets, and prefixed to it an essay on poetry containing much valuable criticism. In 1820 he accepted the editorship of the New Monthly Magazine, and in the same year made another tour in Germany.
Four years later appeared his Theodric, a not very successful poem of domestic life. He took an active share in the foundation of the University of London, visiting Berlin to inquire into the German system of education, and making recommendations which were adopted by Lord Brougham. He was elected Lord Rector of Glasgow University (1826-1829) in competition against Sir Walter Scott. Campbell retired from the editorship of the New Monthly Magazine in 1830, and a year later made an unsuccessful venture with The Metropolitan Magazine. He had championed the cause of the Poles in The Pleasures of Hope, and the news of the capture of Warsaw by the Russians in 1831 affected him as if it had been the deepest of personal calamities. "Poland preys on my heart night and day," he wrote in one of his letters, and his sympathy found a practical expression in the foundation in London of the Literary Association of the Friends of Poland. In 1834 he travelled to Paris and Algiers, where he wrote his Letters from the South (printed 1837). The small production of Campbell may be partly explained by his domestic calamities. His wife died in 1828. Of his two sons, one died in infancy and the other became insane. His own health suffered, and he gradually withdrew from public life. He died at Boulogne in 1844 and was buried in Westminster Abbey.