As elsewhere in Wales, the Laws in Wales Acts 1535 and 1542 provided Anglesey with two members of parliament, one representing the county and the other representing a borough constituency named after the county town but including other "contributory boroughs" who were jointly responsible for providing for the upkeep of the MP and, in return, were granted a say in his election.
Porritt, the early 20th century expert on the history of the Unreformed House of Commons, concludes that "the probability is that Newborough broke the connection in a fit of ill-humour" rather than that it was contrived by Beaumaris; but within a few decades, as the desirability of being directly represented in Parliament became more widely recognised, Newborough was trying unsuccessfully to regain its former status.
The franchise was further restricted in 1562, when Elizabeth I granted Beaumaris a new municipal charter, which reserved the right to vote in parliamentary elections to members of the town corporation.
Thereafter until 1832, Beaumaris was a closed "corporation borough" of a type common in England but unknown elsewhere in Wales; its only voters were the mayor, two bailiffs and 21 "capital burgesses", and since they had the sole right to fill any vacancies arising in their number their power was entirely self-perpetuating, making the constituency a completely safe pocket borough.
For the best part of two centuries before the Great Reform Act 1832, the nomination was in the hands of the Bulkeley family of Baron Hill, and the elections were never contested.