It returned one Member of Parliament (MP) to the House of Commons of the Parliament of the United Kingdom, elected by the first past the post system from 1918 to 1950.
Spennymoor was created under the Representation of the People Act 1918 for the 1918 general election, comprising southern parts of the abolished Mid Division of Durham, including the communities of Brandon, Brancepeth, Tudhoe and Willington.
Spennymoor was added from Bishop Auckland and Crook and Tow Law from Barnard Castle.
It was abolished for the 1950 general election under the Representation of the People Act 1948, with the bulk of the constituency being included in the re-established constituency of North West Durham, with the exception of the town of Spennymoor itself, which was transferred to Durham.
The political parties had been making preparations for an election to take place from 1939 and by the end of this year, the following candidates had been selected;