After graduating Sollas spent six years as a University Extension Lecturer, publishing a syllabus of lectures in 1876 on geology and biology, and in 1879 became lecturer in Geology and Zoology at University College, Bristol. In 1880 he was made Professor of Geology. In 1883 Sollas left Bristol to take up a position as Professor of Geology at Trinity College Dublin, where he remained until he was made Professor of Geology at the University of Oxford in 1897. At Oxford his main contribution was significantly expanding the Geology department, appointing new demonstrators and lecturers and employing his own daughters as unpaid research assistants. At the same time he did research in a variety of fields, and was described as "one of the last true geological polymaths".
