Salvatore Anello, from Indiana, pleaded guilty to negligent homicide Thursday.
He had consistently protested his innocence over granddaughter Chloe's death.
The 18-month-old girl died July 2019 after falling 150ft from a cruise ship window.
The grandfather of an 18-month-old girl who plunged to her death after falling from a window of a cruise ship in Puerto Rico last year, has pleaded guilty to negligent homicide.
Salvatore 'Sam' Anello of Valparaiso, Indiana, admitted to the charges on Thursday after initially pleading not guilty last October.
The 51-year-old was charged with the death of granddaughter Chloe Wiegand who died after falling 150 feet from a docked Royal Caribbean cruise ship in July 2019.
Anello had been holding the little girl up to an open window on the 11th deck of the Freedom of the Seas ship, when she slipped from his grasp and fell to her death.
Anello announced his decision to change his plea earlier this year in hopes of moving on from the tragedy after reaching an agreement with prosecutors that involved no jail time.
'I took a plea deal today to try to help end part of this nightmare for my family, if possible,' he said in a statement in February.
Puerto Rico prosecutor Laura Hernández said Anello would be sentenced on December 10.
'We have found justice for Chloe,' she said.
Anello's attorney, Michael Winkleman, did not immediately return a message for comment.
Anello has repeatedly said he did not know the window in the children's play area was open and that he lifted Chloe up to it so she could knock on the glass like she had done at her brother's hockey games.
'I wasn't drinking and I wasn't dangling her out of a window,' he said in a previous statement. He also said he is colorblind and might not have realized the tinted window was open.
The girl's parents sued Royal Caribbean last year and accused the company of negligence.
In response, Royal Caribbean said that surveillance video shows Anello leaning out the window for about eight seconds before lifting the girl by and out of the open window for 34 seconds before he lost his grip.
The family said it would have been physically impossible for Anello to lean out like that.
Royal Caribbean did not immediately respond to a request for comment on Thursday.