Mackintosh was soon absorbed in the question of the time, the
French Revolution. In April 1791, after long meditation, he published his
Vindiciae Gallicae: A Defence of the French Revolution and its English Admirers, a reply to
Edmund Burke's
Reflections on the Revolution in France. It placed the author in the front rank of European publicists, and won him the friendship of some of the most distinguished men of the time. The success of the
Vindiciae finally decided him to give up the medical for the legal profession. He was called to the bar in 1795 and gained a considerable reputation there as well as a tolerable practice.
Vindiciae Gallicae was the verdict of a philosophic
liberal on the development of the
French Revolution up to the spring of 1791. The excesses of the revolutionaries compelled him a few years later to oppose them and agree with Burke, but his earlier defence of the
rights of man is a valuable statement of the cultured Whig's point of view at the time. Mackintosh was the first to see Burke's
Reflections as "the manifesto of a counter revolution".
Charles James Fox singled out Mackintosh's book as that which did most justice to the French Revolution, and he preferred it over Burke and
Thomas Paine. After Paine's
Rights of Man, Mackintosh's book was the most successful reply to Burke and Burke's biographer
F. P. Lock considers it "one of the best of the replies to Burke, in some respects superior to
Rights of Man". The poet
Thomas Campbell claimed that had it not been for Mackintosh's book, Burke's anti-revolutionary opinions would have become universal amongst the educated classes and that he ensured that he became "the apostle of liberalism". Mackintosh wrote to Burke on 22 December 1796, saying that "From the earliest moments of reflexion your writings were my chief study and delight...The enthusiasm with which I then embraced them is now ripened into solid Conviction by the experience and meditation of more mature age. For a time indeed seduced by the love of what I thought liberty I ventured to oppose your Opinions without ever ceasing to venerate your character...I cannot say...that I can even now assent to all your opinions on the present politics of Europe. But I can with truth affirm that I subscribe to your general Principles; that I consider them as the only solid foundation both of political Science and of political prudence". Burke replied that "As it is on all hands allowed that you were the most able advocate for the cause which you supported, your sacrifice to truth and mature reflexion, adds much to your glory". However, in private Burke was sceptical of what he considered Mackintosh's "supposed conversion". Burke invited Mackintosh to spend Christmas with him at his home in Beaconsfield, where he was struck by Burke's "astonishing effusions of his mind in conversation. Perfectly free from all taint of affectation...Minutely and accurately informed, to a wonderful exactness, with respect to every fact relative to the French Revolution". When Mackintosh visited Paris in 1802 during the
Peace of Amiens, he responded to compliments from French admirers of his defence of their revolution by saying: "Messieurs, vous m’avez si bien refuté". ==Lawyer==