He espoused Macaulay's staunch liberal Whig principles in accessible works of literate narrative unfettered by scholarly neutrality, his style becoming old-fashioned in the course of his long and productive career.

Whigs and Liberals believed the common people had a more positive effect on history than did royalty and that democratic government would bring about steady social progress.

[3] On his paternal side, he was the third son of Sir George Trevelyan, 2nd Baronet, who had served as Secretary for Scotland, under Liberal Prime Ministers William Gladstone, and the Earl of Rosebery, and the grandson of Sir Charles Trevelyan, 1st Baronet, who had served as a civil servant and had faced considerable criticism for his and the British government's handling of the Great Famine of Ireland.

[3] Trevelyan made his own reputation by depicting Italian patriot Giuseppe Garibaldi as a great hero who stood for British ideals of liberty.

For Trevelyan, Garibaldi was the champion of freedom, progress, and tolerance, who vanquished the despotism, reaction, and obscurantism of the Austrian empire and the Neapolitan monarchy.

The books were also notable for their vivid evocation of landscape (Trevelyan had himself followed the course of Garibaldi's marches), for their innovative use of documentary and oral sources, and for their spirited accounts of battles and military campaigns.

[7]Historian Lucy Voakes argues that his Garibaldi project was part of a larger movement among English intellectuals to consolidate, celebrate and sometimes critique liberal culture and politics.

She sees Trevelyan's conception of the hero, and his study of the Italian Risorgimento emerging from his promotion of a distinctly "English" patriotism based upon Whig gradualism, parliamentary monarchy and a hierarchical anti-republicanism.

Shocked by the horrors of the Great War he saw as an ambulance driver just behind the front lines, Trevelyan became more appreciative of conservatism as a positive force, and less insistent that progress was inevitable.

Cannadine says he reported they were "the nation's evolution and identity: parliamentary government, the rule of law, religious toleration, freedom from continental interference or involvement, and a global horizon of maritime supremacy and imperial expansion".

[12]During World War I, Trevelyan commanded a British Red Cross ambulance unit on the Italian front;[13] his defective eyesight meant he was unfit for military service.