Chafing at the restrictions imposed by the German foreign ministry, Harrison resigned from Reuters in 1904 and expressed his concerns about the Kaiser in his first book, The Pan-Germanic Doctrine.

Returning to London, he worked briefly as a freelance journalist until he was offered the editorship of The Observer by Lord Northcliffe, the weekly newspaper's new owner.

At the end of 1908, Harrison accepted an offer from Alfred Mond to assume the editorship of the newly acquired literary magazine The English Review.

During this time he broadened the range of contributors, publishing works by authors as diverse as Anton Chekhov, Hermann Hesse, Katherine Mansfield, Aleister Crowley, Edward Gordon Craig, George Bernard Shaw, and William Butler Yeats.

Politics was also a topic addressed in the pages of The English Review, and Harrison continued to warn readers about the threat posed by Germany in the years leading up to The First World War.