When the state of Ulster became such that a Protestant who remained there could hardly avoid being either a rebel or a martyr, Leslie fled to London.

His abilities and his connections were such that he might easily have obtained high preferment in the Church of England.

But he took his place in the front rank of the Jacobite body, and remained there stedfastly, through all the dangers and vicissitudes of three and thirty troubled years.

Though constantly engaged in theological controversy with Deists, Jews, Socinians, Presbyterians, Papists, and Quakers, he found time to be one of the most voluminous political writers of his age.

Of all the nonjuring clergy he was the best qualified to discuss constitutional questions.