Allom began his career working for the architect Francis Goodwin. He spent over seven years in Goodwin's office (1819-1826) and then went on to study at the Royal Academy Schools, where he worked on designs for churches, workhouses, and a military asylum.
While at the Royal Academy, Allom began to exhibit his work, a practice he continued until the end of his life. In 1834, Allom was one of the founders of the Royal Institute of British Architects, where he worked on various projects, including the Houses of Parliament, Highclere, and the Thames Embankment.
The majority of Allom's works are well suited to reproduction and were made with the engraver in mind. He traveled extensively and over the course of his career contributed hundreds of illustrations for travel and topographical books.