 At the 1868 general election, Merthyr Tydfil became a two-member constituency with a much-increased electorate as a result of the Second Reform Act of 1867.Since the formation of the constituency, Merthyr Tydfil had dominated representation as the vast majority of the electorate lived in the town and its vicinity, whereas there was a much lower number of electors in the neighbouring Aberdare Valley.During the 1850s and 1860s, however, the population of Aberdare grew rapidly, and the franchise changes in 1867 gave the vote to large numbers of miners in that valley,

The middle-classes of the Aberdare Valley sought the right to select a second Liberal candidate and their choice soon fell upon Fothergill.