Menendez was appointed to the San Antonio Zoning Commission for District 6 in 1994. In 1997, after a heated campaign, he was elected to the District 6 seat on the city council. In 1999, Menendez was re-elected to the council with more than 84 percent of the vote. He served on the Small Business, International, and Ethics committees. He also was the chairman of the City's Community Revitalization Action Group. In 2000, term-limited on the council, he ran for the state House of Representatives and was sworn into his first term in 2001. As a representative, Menendez headed the House Committee on Defense and Veterans' Affairs, which put him in contact with thousands of Texas veterans and provided a basis for his successful run thereafter for the Texas Senate. Menendez won election to a full term in the state Senate in the Democratic primary on March 1, 2016, when he defeated his former opponent, Trey Martinez Fischer, who, this time gave up the District 116 House seat, Fischer held, to run for the Senate. A number of lobbyists and political action committees which had supported Martinez Fischer switched allegiance to the incumbent Menendez, whose campaign chairman, Colin Strother, worked in numerous successful campaigns; among them U.S. Representative Henry Cuellar of Laredo in Texas' 28th congressional district. Menendez faced no Republican opposition in his heavily Democratic district. In a debate before the American Association of Retired Persons in San Antonio, Menendez noted that Martinez Fischer would have become dean of the Bexar Countystate House delegation had he remained in the House. Martinez Fischer did assume the Bexar County legislative dean's position on February 1, 2016, with the retirement of colleague Ruth McClendon. "Trey did a great job in the House killing many, many bills... We have differences of opinion, we debate. We're passionate about it, but we're also respectful about it," said Menendez. Buoyed by the power of incumbency for just a year, Menendez defeated Martinez Fischer, 31,046 votes to 21,383. On the last day of the regular legislative session in 2017, Menendez used a filibuster to kill a bill supported by Republican Donna Campbell of New Braunfels, which would have made it more difficult for municipalities to annex surrounding territory. In the 2017 special legislative session, Menendez spoke against a bill to increase the penalty from misdemeanor to felony when one is convicted of intentionally submitting false information on a mail-in ballot application. Menendez argued that such legislation would lead to "unintended consequences." Kelly Hancock, a Republican senator from North Richland Hills in Tarrant County, argued that the legislation is needed because mail-in voting has been linked to illegal voting and election fraud.