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".