The seat is most famous as the location of William Ewart Gladstone's upset victory in the Midlothian Campaign of 1880, regarded as the birth of the modern political campaign in the United Kingdom. After Gladstone's victory it became the first non-English constituency to be represented by a serving prime minister.
In 1801 the Parliament of Ireland was merged with the Parliament of Great Britain to form the Parliament of the United Kingdom . The first general election of the new parliament was the general election of 1802. There was no change to the boundaries of any pre-existing Westminster constituency, and 1802 boundaries were used also in the general elections of 1806, 1807, 1812, 1818, 1820, 1826, 1830 and 1831.
For the 1832–33 general election, as a result of the Representation of the People Act 1832, the constituency was redefined. The boundaries of counties and burghs for parliamentary purposes ceased to be necessarily those for other purposes, but nominally the Edinburghshire constituency consisted of the county of Edinburgh minus the burghs of Edinburgh, Leith, Portobello, and Musselburgh. Edinburgh was again covered by the Edinburgh constituency, and Leith, Portobello and Musselburgh were covered by the Leith Burghs constituency.
The Midlothian and Peebles Northern constituency consisted of the Calder and Suburban districts and part of the Lasswade district of the county of Midlothian, and the Peebles and Southern constituency consisted of the county of Peebles, the Gala Water district and part of the Lasswade district of county of Midlothian, and the burghs of Bonnyrigg, Lasswade, and Penicuik in county of Midlothian.[1]