The decision follows last week's four-day hearing, where convicted killer Thomas Provenzano and his attorneys tried to prove the chair didn't work properly when Allen "Tiny" Davis was put to death last month.
Davis' nose bled at the moment of electrocution, which led critics to say that the voltage used to execute the 344-pound man was inadequate.
Judge Clarence Johnson ruled that the chair functioned as it was designed and that it is not cruel or unusual punishment. Defense attorneys continue to argue that opinion.
Johnson concluded that Davis' nosebleed began before the electric current was applied and the chair worked as intended.
He acknowledged that executions in the chair provoked "emotional responses such as fear and dread" and involved "some necessary pain and discomfort" as straps were tightened to hold the condemned prisoner in place.
But he said Davis "suffered instantaneous and painless death once the current was applied to him." Davis was executed for killing a pregnant woman and her two young daughters in 1982.
Barring a higher court ruling, Johnson's decision would allow Provenzano to be executed after his stay expired Sept. 14.
However, the ruling now goes to the Florida Supreme Court. The justices will make the final decision on whether use of the electric chair is constitutional at the end of August.
Florida's electric chair has come under increased scrutiny since flames shot from the head of a condemned prisoner during a March 1997 execution, the second such incident in 10 years.
Before Davis' execution, the state replaced the 76-year-old oak electric chair, dubbed Old Sparky. But only the wooden chair was new. The electrical equipment was not replaced.
Of the 38 states where capital punishment is allowed, Florida is the largest of the four where electrocution is the sole method of execution. Since 1924, 240 inmates have died in Florida's electric chair, including serial killers Ted Bundy and Judias Buenoano, who in 1998 became the first woman executed in the chair.
Florida, which has 375 prisoners on death row, leads the nation in the number of death sentences revoked.