In a brief statement, the Maricopa County Sheriff's Office said Officer Gene Lee died from his injuries suffered in the Tuesday morning attack.
"Earlier tonight, Detention Officer Lee, surrounded by his family, passed away," it said. "Under these tragic circumstances and out of respect for the Lee family, MCSO will not be making any further statements tonight. Please keep the entire Lee family, friends and his MCSO colleagues in your thoughts and prayers during this difficult time."
The inmate accused of attacking Lee, identified as Daniel Davitt, 59, has been transferred to a jail in another county, authorities said. Lee, a six-year veteran with the department, hit his head on the floor in the Lower Buckeye Jail when Davitt allegedly swept the officer's legs out from under him.
"While at work, without any initial interaction leading him to believe there's a potential threat, he was attacked by an inmate," Sheriff Paul Penzone said at a news conference Wednesday.
"The inmate caught him off-guard, grabbed him by his throat and then swept his legs out from under so aggressively that when he was knocked off balance and thrown to the floor, the first part of his body to strike the cement was his head," he added.
Davitt was awaiting trial on sex crimes involving children and had been custody for two years, Penzone said.
"He is nothing more or less than a criminal predator with no respect for authority, for human life, for the community," he said.
Arizona Gov. Doug Ducey ordered flags at all state buildings lowered to half-staff Thursday.
The Associated Press contributed to this report.