Incumbents Al Green (D) and Christian Menefee (D) advanced to a May 26 runoff after neither received more than 50% of the vote in the Democratic primary for Texas' 18th Congressional District on March 3, 2026. As of March 2026, Green and Menefee led the candidate field in local media attention.

The primary took place in the context of redistricting in Texas ahead of the 2026 elections. As of March 2026, this race was projected to be one of two incumbent-versus-incumbent U.S. House elections in 2026.

Green was elected to represent the 9th District in 2024 and ran for re-election in the 18th District after redistricting shifted the 9th District towards Republicans and moved Green's home address into the 18th District. Sylvester Turner (D) was elected to represent the 18th District in 2024. Turner died in March 2025. Menefee defeated Amanda Edwards (D) in the January 31 special runoff election for the remainder of Turner's term. The runoff took place in the 2024 version of the 18th District.

Green was first elected to the House in 2004. Green worked as an attorney in private practice and served as president of the Houston branch of the NAACP. Green ran on his record: "You know that I will stand up to Donald Trump because you saw me do it...You know that I will fight for your health care because you’ve seen me do it. You know that I believe in raising the minimum wage to $25 an hour, because you’ve heard me say it."

Menefee was elected to represent the 18th District in a January 31 special election and previously served as Harris County Attorney. Menefee said he was running "because working people deserve a government that has their back...Christian has spent his career fighting back against bullies, and he’s ready to do it in Washington."