Joaquin Castro is an American lawyer and Democratic politician who has represented Texas's 20th congressional district in the United States House of Representatives since 2013. The district includes just over half of his native San Antonio. He currently serves on the United States House Committee on Foreign Affairs and the United States House Permanent Select Committee on Intelligence.

The 2018 United States Senate election in Texas was held on November 6, 2018, along with other elections to the United States Senate and elections to the United States House of Representatives in additional states. Incumbent Republican U.S. Senator Ted Cruz won re-election to a second term defeating Democratic candidate Beto O'Rourke. The primary for all parties was held on March 6, 2018, making it the first primary of the 2018 season. As Cruz and O'Rourke both won majorities in their primaries, they did not participate in the May 22 runoff primary that was held for some nominations in Texas.