The original site of the Northampton Institute comprised one and a half acres donated by the 4th Marquess of Northampton and his son. The area faced St John Street, Ashby Street and Lower Charles Street, London, on the site of the former Clerkenwell Manor House, subsequently used as a school and lunatic asylum. The Institute's first building was designed by the architect Edward W Mountford (1855-1908), later the architect of the Old Bailey. The foundations were laid in 1894, with gradual use of the facilities as completed until the official opening of the building in 1898 by the Lord Mayor of London. Extensions were provided in the courtyard of the building for Metallurgy in 1898 and Mechanical Engineering in 1901. The Governing Body authorised the building of a five storied block in the residue of the courtyard in 1908, completed and opened by the Earl of Halsbury in the following year. However growth of the Institute placed greater pressures on existing accommodation, and loans from the New River Company and Skinners' Company provided the means to provide a site for an annex by the purchase of houses on the west side of St John Street in 1908. The intervention of war and economic depression prevented the exploitation of this site until an extension fund was started in 1927. Work began in 1930, and the Connaught Building was opened in 1932 by Prince George, Duke of Kent. It occupied around half the annex site and provided accommodation for chemistry, clockmaking, furriery, a lens workshop, automobile laboratories and general classrooms. Work started on extensions and additional floors to the Connaught Building from 1938 but was curtailed by the coming of war.
The next major phase of development was carried out during from 1949, when it was proposed a further site in St John Street be acquired, the Great Hall be rebuilt, and the Gymnasium block was also to be rebuilt to provide five stories for engineering workshops, classrooms, a staffroom and new library. The site in St John Street was replaced by another in Spencer Street and work started in 1950. The new library was opened in 1955, as was the new Great Hall. The new hall block provided new laboratories in the basement. The new development was officially opened by Sir David Eccles, the Minister of Education, in 1956. In 1959 work started on adding two extra floors were added to the Connaught Building to provide extra laboratories for chemistry and additional classrooms. These were opened by Lord Fleck in 1961.
At the same time a larger development was planned on a site on the north east corner of the Connaught site. The first phase was to comprise the Electrical Building, High Voltage Laboratory and refectory block, followed by a new library, Student's Union, lecture theatres and a new hall. These were completed and handed over during the period 1969-1970, and opened by the Chancellor, Col Sir Ian Bowater, in Nov 1970.
The next development (subsequently named the Tait Building), was to comprise a new Civil and Mechanical Engineering Building and lecture theatre). Construction began in 1971 and it was opened by Dr O A Kerensky in 1974.
Northampton Hall, the first hall of residence, opened in 1964, followed by the Finsbury hall of residence on the Goswell Road site, which opened in 1972. The Saddlers' Sports Centre was opened in 1974, and another hall of residence, Heyworth Hall, was in use by 1977. The City Parochial Foundation provided the funding for the purchase of six acres of land in Oakthorpe Lane, Palmers Green, North London, in 1906, to use as playing fields for the Institute.