The 1903 Barnard Castle by-election was a parliamentary by-election held for the British House of Commons constituency of Barnard Castle, in County Durham, on 24 July 1903.

Barnard Castle was a county constituency centred on the town of Barnard Castle in County Durham, which returned one Member of Parliament (MP) to the House of Commons of the Parliament of the United Kingdom. It was created for the 1885 general election and abolished for the 1950 general election.