William Embre Gaines (born August 30, 1844) was a Republican politician who represented Virginia in the United States House of Representatives during the late nineteenth century. Serving as a member of Congress from Virginia’s 4th Congressional District, he held office as a Representative for a single term. His tenure in the U.S. House began on December 5, 1887, and concluded on March 3, 1889.

Gaines’s service in Congress placed him among the historical members of the House from Virginia during a period of post–Civil War political realignment and reconstruction-era aftermath, though specific details of his legislative activity, committee assignments, or policy priorities are not provided in the available record. Identified in congressional records by the bioguide ID G000009, he is noted primarily for his one-term service and his affiliation with the Republican Party. Further personal, professional, or post-congressional details are not contained in the existing metadata.