The franchise in Mitchell was a matter of controversy in the 17th century, but was settled by a House of Commons resolution on 20 March 1700 which stated "That the right of election of members to serve in Parliament for the Borough of St Michael's, in the County of Cornwall, is in the portreeves, and lords of the manor, who are capable of being portreeves, and the inhabitants of the said borough paying scot and lot": this gave the vote to most of the male householders.
The borough was often not in the complete control of a single proprietor, the voters being swayed between those of the lords of the manor from whom they expected to receive most benefit in return.
Admiral Boscawen..., by supplying some of the voters with money and conferring favours on others, seems to be adding very considerably to the strength of his interest.
The proprietors by the 1820s were the Earl of Falmouth (a Boscawen) and Sir Christopher Hawkins, Hawkins having purchased his interest some years previously from Sir Francis Basset; but Mitchell having thus been reduced to one of the smallest of all the rotten boroughs (in 1831, the borough had a population of approximately 90, and 23 houses), it was naturally disfranchised by the Reform Act 1832.
Mitchell's early MPs included the explorer and statesman Walter Raleigh, who sat briefly for the borough in the 1590s while out of favour at court and so unable to secure a more prestigious seat.