2010-2012

In 2010, when incumbent State Representative Juan-Carlos Planas was unable to seek re-election, Díaz ran to succeed him in the 115th district, which narrowly stretched from Doral to Cutler Ridge in Miami-Dade County. He faced Kendall Community Councilwoman Carla Ascencio-Savola in the Republican primary, and he campaigned on improving the quality of living in the district, noting, "It's an important time to make this area, this district, better. People have lost confidence in where they live," and on his lack of experience in politics, declaring, "People have rallied around the fact that I'm not the same-old, same-old in the district."^[4] Ultimately, Díaz defeated Ascencio-Savola by a comfortable margin, winning 60% of the vote to her 40%. He advanced to the general election, where he was opposed by Jeffrey Solomon, the Democratic nominee and Christopher Blau, the Tea Party nominee. Neither of his opponents proved to be a significant obstacle, however, and Díaz easily defeated both of them in a landslide, winning 64% of the vote to Solomon's 33% and Blau's 3%.

2012-2017

When the state's legislative districts were redrawn in 2012, Díaz was drawn into the 116th district, which contained most of the territory that he had previously represented in the 115th district. He faced fellow State Representative Ana Rivas Logan in the Republican primary, and an extremely contentious election ensued. Díaz accused Logan of having her campaign workers tell voters that he was gay, was "pro-abortion" and "voted for a 15-percent increase" in university tuition, while Logan alleged that Díaz's campaign made calls to voters in the district, telling them, "Don't vote for her. She's a Nicaraguan. Your commitment is with the Cuban vote."^[5] Despite the rancor of the race, however, it was not close, with Díaz winning the nomination with 66% of the vote to Logan's 34%. Advancing to the general election, he only faced write-in opposition and won re-election with nearly 100% of the vote.

In 2013 Díaz was mentioned as a potential candidate to run against Democratic United States Congressman Joe García in the 26th Congressional District,^[6] he ultimately declined to run, instead opting to run for re-election.

Díaz served as the Chair on the Florida House Regulatory Affairs Committee. He was also a member of the Florida House Appropriations Committee, K-12 Subcommittee, and the Local Government Affairs Subcommittee.^[7] In January 2016, the Florida House Health Innovation Subcommittee unanimously voted to approve the KidCare legislation sponsored by Díaz, which would allow thousands of children legally residing in Florida to receive health coverage through the KidCare subsidized insurance program.^[8]

In September 2017, Democrat Annette Tadeo won the District 40 election over Díaz.