In 1866 the City of Edinburgh began to redevelop the Old Town and in 1871 the Adam Square building was demolished. Fortunately the School had obtained a new site in Chambers Street and the foundation stone was laid on 9th October 1872. The School continued to expand but needed more money, the solution to which was the merger with George Heriot's Trust which would last until 1927. The new organisation was named Heriot-Watt College. By this point there were 2,000 students, of which 15% were women.

The College's first Principal, physicist Francis Grant Ogilvie, transformed the curriculum introducing new day and evening classes. An increasing demand nationally for classes in science, technology, art, design and commerce was changing further education and the College became the Central Institution for southeast Scotland in 1902. An Associateship of the College soon became equivalent to a degree, and a link with Edinburgh University allowed engineering and science students to also obtain a University degree. Students to benefit from this included athlete Eric Liddell.

The First World War interrupted further development as College resources were put over to support the war effort with munitions production. When James Cameron Smail became Principal in 1928 he led an ambitious programme to build new extensions, a new library and dining hall, common rooms - separate for men and women - and established a Students Representative Council.