Salvatore "Sam" Anello was playing with his granddaughter, Chloe Wiegand, on July 2019 near an open window on the 11th floor while the ship was docked in Puerto Rico.
He was charged with negligent homicide months after the incident and initially pleaded not guilty.
CNN has reached out to Anello's attorney for comment.
Michael Winkleman, an attorney representing Chloe's family, but who does not represent Anello in his criminal case, said Anello changed his plea to guilty as part of a deal with prosecutors.
"This decision was an incredibly difficult one for Sam and the family, but because the plea agreement includes no jail time and no admission of facts, it was decided the plea deal is in the best interests of the family so that they can close this horrible chapter and turn their focus to mourning Chloe and fighting for cruise passenger safety by raising awareness about the need for all common carriers to adhere to window fall prevention laws designed to protect children from falling from windows," he said Thursday in a statement to CNN.
Judge Gisela Alfonso Fernandez accepted Anello's guilty plea, according to the Puerto Rico Department of Justice. A sentencing hearing has been set for December 10.
The details of the toddler's death have been disputed since the accident. Port Authority officials said Anello sat the girl in the window and lost his balance, and the girl fell to her death.
A wrongful death lawsuit filed against the ship's operator, Royal Caribbean Cruises, on behalf of the family, says Anello was supervising Chloe when she wandered to a floor-to-ceiling wall of windows.
She asked to be lifted up to bang on the glass, the suit said, so Anello held her up and she leaned forward. She then slipped through his hands and through the open pane, falling 150 feet onto the San Juan Pier, according to the suit.
The family claims that the glass panes on the deck can be slid open by any passenger, and the walls didn't contain warnings that the panes could open. Anello told CBS News last year that he wouldn't have placed the toddler near the window if he had known it was open.