He was born to a Roman Catholic family in York. He was the brother of Joseph Aloysius Hansom, architect and creator of the Hansom cab, and father of the architect Edward Joseph Hansom. He practised in partnership with his brother, Joseph, in London from 1854. This partnership was dissolved in 1859 when Charles established an independent practice in Bath with his son Edward (born 22 October 1842) as an articled clerk. He took his son into partnership in 1867, by which time the practice had moved to Bristol, with a large West Country practice of church and collegiate architecture. In Bristol he took on Benjamin Bucknall as an assistant.
The original Clifton College buildings were all designed by Hansom.
His first design at Clifton was for Big School (then a meeting hall and now the school canteen) and a proposed dining hall. Only the former was actually built and a small extra short wing was added in 1866. This is what now contains the Marshal's office and the new staircase into Big School.
Hansom was called back to the College in the 1870s and asked to design what is now the Percival Library and the open-cloister classrooms. This project was undertaken in two stages and largely completed by 1875, although the Wilson Tower was not built until 1890.
Our Lady the Immaculate Conception Roman Catholic Church, Devizes, Wiltshire, 1865