Rep. Martinez Fischer graduated from Oliver Wendell Holmes High School, where he played for the nationally-ranked Huskies football team and was named to the school's Hall of Fame. Rep. Martinez Fischer went on to become the first member of his family to receive a college degree, graduating from the University of Texas at San Antonio. He was selected to study as a National Urban Fellow, receiving his Masters in Public Administration from the Baruch College of Public Affairs, City University of New York. Rep. Martinez Fischer earned his law degree from the University of Texas School of Law.

Rep. Martinez Fischer quickly earned a reputation as someone who wouldn't back down from his convictions, becoming one of the most influential and passionate champions for those in need. Texas Monthly perhaps put it best when, in naming Rep. Martinez Fischer one of the 10 Best Legislators in the state in 2013, they declared him "a soldier prepared to do battle but ready to make peace." Though often outnumbered by his opponents, Rep. Martinez Fischer has repeatedly delivered legislative victories for the people of San Antonio, defeating harmful legislation and working to pass job-creating, bipartisan legislation of his own.

Among his most important accomplishments was leading budget negotiations to restore $3.93 billion dollars in public education funding cuts in 2013, despite being outnumbered by the legislative majority in the House. Rep. Martinez Fischer's relentless pursuit on behalf of Texas school children and educators earned him the prestigious "Friend of Education Award" as well as a "Legislative Star" recognition by the Texas Classroom Teachers Association.

Another of Rep. Martinez Fischer's key legislative achievements was his role in passing the 'Boeing Bill,' which created hundreds of good-paying manufacturing jobs in San Antonio to build, test, and repair the Boeing 787 Dreamliner and paved the way for San Antonio to have the honor of repairing and refitting Air Force One for the President of the United States. Rep. Martinez Fischer's work to improve the economy of San Antonio and his talent for legislating earned him the distinguished recognition of being named one of Texas' '20 Latino Political Rising Stars' and one of the '20 Latino Democrats to watch over the next 20 years' by the Houston Chronicle. Rep. Martinez Fischer is one of the best state lawmakers according to Texas Monthly, who named him one of the "10 Best" lawmakers in both the House and Senate three sessions in a row (2011, 2013, 2015). In 2015, the publication also awarded him the 'Bull of the Brazos Award' for being the most effective advocate in the legislature.

Other legislative victories abound- when school supplies were excluded from being eligible for tax-free weekend, Rep. Martinez Fischer passed a middle-class tie-in that included school supplies in the sales tax exemption and made it easier for parents to buy books, backpacks, and pencils for their kids. In 2019, Rep. Martinez Fischer played a leading role in passing Senate Bill 1264, the strictest protections against surprise medical billing in the country. His bipartisan work on this proposal served as the model for the United States Congress when they passed a similar measure. In 2009, Rep. Martinez Fischer also led the push to finally secure funding to build the Tejano Monument on the South Lawn of the State Capitol to honor Tejano history and culture.

As Chairman of the Mexican American Legislative Caucus (MALC), the oldest and largest Latino legislative caucus in the country, Rep. Martinez Fischer led the largest voting rights lawsuit in the nation challenging how Texas congressional and state legislative seats are drawn. Rep. Martinez Fischer and his peers challenged the state in what became the longest voting rights case in Texas history. His relentless pursuit of justice for minority voting rights made him one of the 30 most influential Democrats in Texas by Campaigns & Elections Magazine, and the internationally-acclaimed publication The Economist named Rep. Martinez Fischer among the leaders changing the national political demographic scene in an article titled, "The New Face of America." Outside of politics, Rep. Martinez Fischer is a practicing lawyer in the San Antonio area. He has practiced in front of numerous state and federal courts throughout Texas since his admission to the bar. Rep. Martinez Fischer also served as an appointee to the Intergovernmental Policy Advisory Committee, advising the United States Trade Representative on trade policies that affect state and local governments. He has briefed former President Obama on national voting rights policy and was a frequent invitee to the Obama White House, serving as the First Family's guest on over a dozen occasions and even watching the 2011 Super Bowl with the President and the First Family. Rep. Martinez Fischer and his wife, Elizabeth, who is also a practicing attorney, live together with their daughters Francesca and Camilla in San Antonio's historic West Side. His favorite sport is whatever his girls happen to be playing.