Dean was appointed a Commissioner of Customs for England and Wales in 1810, after Sir Alexander Munro's post on the Board was vacated. At that time,
William Roe was Chairman of the Customs Board, and he was joined in 1813 by
Francis Fownes Luttrell; both men retired in 1819 and Dean became chairman, with
Snowdon Barne as his Deputy. During his long tenure as chairman, he was called to answer questions by Parliamentary Select Committees on a number of occasions. As chairman, Dean has been described as "a remarkable man, extremely clever and industrious, yet eccentric". Nevertheless, the Committee of Inquiry became increasingly critical of the Board and its management during the early 1840s; finding that, of the nine members of the Board, none, except Dean and his deputy, "had done any work worthy the name". In turn, Dean protested to the Committee that their scrutiny of the board should cease; while acknowledging that appointments to it were not meritocratic, he nonetheless defended the men as "gentlemen—men of education". In 1843,
The Times published two articles which heavily criticised the Board and its practices; accusing them of "partiality and vindictiveness", the writer also stated that "with the exception of the chairman and vice-chairman, the Commissioners know as much of the affairs passing through their own departments as their own washerwomen." The Board came to understand that the writer was known to the Committee of Inquiry, prompting Dean and his commissioners to protest over what they claimed amounted to libel; however, the Inquiry pressed ahead. In the criticism which followed, several members "retired"; Dean too retired in 1846, and it is possible that he was prompted to leave under these circumstances. He was succeeded by Sir
Thomas Fremantle in June 1846. ==Personal life==