The gunman identified as Nikolaus Cruz had once been expelled for disciplinary reasons from the Marjory Stoneman Douglas High School in Parkland, north of Miami.
As well as the 17 people killed, a dozen others were injured before Cruz was arrested.
Twelve of the dead were killed inside the school, two others just outside, one more on the street and two other victims died of their injuries at a hospital.
Those who lost their lives included students and adults.
The Valentine's Day carnage in Miami was the latest outbreak of gun violence that has become a regular occurrence at schools and college campuses across the United States over the past several years and was the 18th shooting in a U.S. school so far this year.
Reacting to the shootings U.S. President Donald Trump said on Twitter, "my prayers and condolences to the families of the victims of the terrible Florida shooting. "No child, teacher or anyone else should ever feel unsafe in an American school."