Richardson attended the City of Westminster School and, at the age of 16, entered HM Civil Service in 1899 as a boy clerk.
This postgraduate degree explored English medieval economic thought and in 1912 his researches earned him the Royal Historical Society's Alexander Prize.
[4] In 1926, Richardson travelled to France to carry out research, which resulted in the publication of one of his most important articles: "The Origins of Parliament", which appeared in the Transactions of the Royal Historical Society in 1928.
The year before, he had begun collaborating with the historian G. O. Sayles, with whom he worked on numerous projects relating to the history of the English parliament, laws and government.
Richardson alone wrote articles and reviews as well as The English Jewry under the Norman Kings (1960); he was involved in studying the medieval legal scholar Henry de Bracton's treatise.
His daughter Helen (married name Suggett) was also a historian, who, like her father, received the Alexander Medal in 1945 for her essay "The Use of French in England in the Later Middle Ages".