Sir Charles Herbert Reilly (4 March 1874 – 2 February 1948) was an English architect and teacher. After training in two architectural practices in London he took up a part-time lectureship at the University of London in 1900, and from 1904 to 1933 he headed the University of Liverpool School of Architecture, which became world-famous under his leadership. He was largely responsible for establishing university training of architects as an alternative to the old system of apprenticeship.

Reilly was a strong and effective opponent of the Victorian Neo-Gothic style, which had dominated British architecture for decades. His dominance also ended the briefer popularity of the Arts and Crafts and Jugendstil movements in Britain, earning him the enmity of Charles Rennie Mackintosh, an exponent of the latter. For many years Reilly favoured a form of Neo-Classicism strongly influenced by developments in American architecture. Later in his career, he embraced the principles of the modernist movement, and of town planning for social and aesthetic improvement.

As a practising architect, Reilly was responsible for few well-known buildings. His influence on British architecture came through the work of his pupils, who included Herbert Rowse, Lionel Budden, William Holford and Maxwell Fry. Among his students were future professors of architecture and heads of architectural colleges in Britain, Canada and Australia; buildings were commissioned from Reilly pupils throughout the British Empire and beyond.

Reilly was born on the Seven Sisters Road in Manor House, London, the son of the architect and surveyor Charles Reilly (1844–1928) and his wife Annie, née, Mee. Whilst Reilly was still very young, the family moved to a large Regency period house, just nearby on Woodberry Down. His family remained in the same house for the next two decades He was educated at a preparatory school in Hove between the ages of nine and 13, and then at Merchant Taylors' School, London, and Queens' College, Cambridge. As an undergraduate he helped to found the Cambridge branch of the Fabian Society; he retained his left-leaning views all his life. After graduating with a first class degree in mechanical science, he worked for two years as an unpaid draughtsman at his father's office, and then joined the office of John Belcher as an "improver".

In 1898, Reilly became an Associate of the Royal Institute of British Architects (RIBA). In 1900 he applied for the chair of architecture at King's College, London; he had not seriously expected to be successful and was surprised and pleased to reach the final shortlist of three. The successful candidate, Ravenscroft Elsey Smith, appointed him to a part-time lectureship and introduced him to Stanley Peach, who specialised in designing power stations. Peach and Reilly entered into a joint practice. According to Reilly, Peach was "a good constructor, but diffident about his own powers of design. The result was that he tried far too hard to dress up his engineering buildings, with their fine roofs and great chimneys, with 'architecture' when they would have been much better left alone." Reilly, on the other hand, was more interested in design than in the mechanics of construction.

In 1902, Reilly applied unsuccessfully for the chair of architecture at University College, London. In the same year he entered the open competition for the design of the proposed new Liverpool Cathedral. He detested the Victorian Neo-Gothic style, describing the work of a leading proponent, Alfred Waterhouse, as having the "colours of mud and blood". His proposed design was in the English Neo-Classical style, with a large central dome in the tradition of Wren's St Paul's. The assessors of the competition were G F Bodley, a leading exponent of the Gothic style, and Norman Shaw. Reilly's design was one of eight highly commended entries that failed to gain inclusion in the final shortlist of five; it was the only classical design among them. Giles Gilbert Scott's Gothic design was the eventual winner, but Reilly had made influential contacts in Liverpool, where much of his career came to be centred.

In the years before and after the turn of the century, architecture in Britain was dominated by an exclusive set of affluent partnerships. Aspiring architects who could afford to buy an articled pupillage in one of the leading firms had an enormous advantage. In an attempt to offer an alternative route into the profession, the University College of Liverpool, the forerunner of Liverpool University, set up a degree course in architecture in 1894. The first professor was Frederick Moore Simpson, a proponent of the Arts and Crafts style of building, which Reilly regarded as "a partial but insufficient remedy for Victorian failure."

In 1904, Reilly was invited to succeed Simpson as Roscoe Professor of Architecture at Liverpool. He held the post for 29 years, retiring in 1933. In 1904 he was lecturing to classes of 11 students, mostly drawn from Liverpool and its environs. He built up the annual intake over the years of his tenure; The Times obituarist wrote "In the ten years up to the 1914–18 war he made the Liverpool School of Architecture a thriving and influential institution to which students would come from the ends of the earth". Reilly lengthened the course to five years, and secured for his students exemption from the RIBA's intermediate examination, and later (1920) from its final examination also. He founded the degrees of Bachelor and Master of Architecture. He was supportive of women studying architecture, and Norah Dunphy, the first woman in the UK to graduate in architecture did so while he was head of school.