The 1903 South Antrim by-election was held after the sitting Unionist MP William Ellison-Macartney had left the Commons to take up the post of Deputy-Master of the Royal Mint.
The by-election was caused by the resignation in January 1903 of the sitting Unionist MP, William Ellison-Macartney, after he had been appointed Deputy-Master of the Royal Mint.
By the early 1900s, his popularity in the constituency had dropped considerably due to his reluctance to dispense favour upon Antrim during his time as a junior minister, and he was criticised by the Belfast newspaper The News Letter.
His opponent was Dr. Samuel Robert Keightley, a Russellite who was the nominee of the Ulster Farmers′ and Labourers′ Union.
He was also backed by the previous independent unionist candidate, Samuel Lawther (who was by 1903 High Sheriff of Belfast).