The 1880 Caernarvonshire by-election was a parliamentary by-election held for the UK House of Commons constituency of Caernarvonshire in Wales on 2 December 1880.
The by-election was caused by the resignation of the sitting Liberal MP, Watkin Williams, who was appointed as a judge of the Queen's Bench Division of the High Court of Justice.
Two candidates were nominated by the two main parties of the time.
The Liberal Party nominated businessman William Rathbone.
The Conservative Party nominated Welsh landowner and magistrate Hugh Ellis-Nanney.