Joseph Addison became his friend, and obtained for him the post of governor to a son of the Duke of Queensberry at a salary of £40 a year.
When Richard Steele discontinued The Tatler, a continuation by Harrison suggested itself to Henry St. John and Swift, who was however dubious.
Between these dates, Swift introduced Harrison to St. John, who obtained for him the post of secretary to Lord Raby, the ambassador extraordinary at The Hague to arrange the treaty with France.
St. John gave him fifty guineas for the expenses of his journey, and on 20 April 1711 he set off for Holland.
In time, but after some trouble with the previous holder of the office, he became queen's secretary to the embassy at Utrecht, and in January 1713 returned to England with the barrier treaty.