Fernández was born in Santa Clara, Cuba. He made three unsuccessful attempts at defecting to the United States before he finally succeeded in 2008. He enrolled at Braulio Alonso High School in Tampa, Florida, and was selected by the Marlins in the first round of the 2011 MLB draft. Fernández made his MLB debut with the Marlins on April 7, 2013. He was named to the 2013 National League All-Star Team, and won the National League (NL) Rookie of the Month Award in July and August. After the season, he won the NL Rookie of the Year Award and finished third in Cy Young Award balloting. He underwent Tommy John surgery during the 2014 season and was named to his second All-Star Game in 2016.