This thesis reestablishes the importance of Thomas Archer as a Baroque architect, after centuries of exclusion from mainstream architectural history. It also strives to rehabilitate Archer into commentary on the wider English Baroque, acknowledging his uniqueness and importance within such a key movement in architectural history. All too often, Archer has been sidelined due to his being classed as a gentlemen architect, with financial independence derived from his Court position as Groom Porter. However, Archer was a skilled designer, who knew and worked alongside the major architectural figures of the period. He produced some of the finest Baroque country houses, churches and garden buildings in this country. The main volume of the thesis takes a fresh look at Archer's major documented works, on a caseby- case, chronological basis. This approach allows each architectural work to be examined within the context of his developing style, which gradually became bolder, and more overtly influenced by the continental Baroque, throughout his lifetime. It also allows the works to be understood within the evolution of Archer's career in Court, which gave him consistent access to some of the most influential members of the gentry in the country; a continuous theme throughout the thesis is a consideration of Archer's patrons, underlining how pivotal his Groomporterage was in securing architectural commissions. Where relevant, the thesis highlights Archer's awareness of designed landscapes, and raises the possibility that he played an active role in advising patrons about the layout of the gardens surrounding his garden buildings and country houses. This is supported by new evidence of Thomas Archer's Grand Tour across Europe, which evidently took in some of the most influential continental gardens of the period. Archer's Grand Tour itinerary also helps elevate his status as an architect, by confirming that he was far better travelled than most of his famous architectural peers, and had seen the Roman Baroque at first hand. The Appendices contain further case studies of some of the most important architectural works that are confidently attributed to Archer, permitting a greater depth of understanding of his style and patronage. A Gazetteer also helps to build up a more detailed chronology of his life and works, and flags up areas for further future research. The Conclusion firmly re-establishes Archer as one of the most important English Baroque Architects, pinpoints the keys to his success, and examines the demise of his career within the context of the Palladian Revival.