In early life, Big Baby belonged to an owner named Daisy, along with Lotso and Chuckles. Then, one day, after a picnic, Daisy fell asleep and drove away, accidentally leaving Lotso, Big Baby, and Chuckles behind. But Lotso and the others went on their way back to Daisy's house, but it was too late when Lotso discovered that he was replaced with another Lots-o-Huggin' Bear. He took Big Baby away from Daisy's house, and he and Lotso took over Sunnyside and turned it into a prison.
Later on, when Woody and the gang were escaping Sunnyside, Lotso and Big Baby caught up with them, and Woody showed Lotso and Big Baby the locket that says "My heart belongs to Daisy", but Lotso didn't care and snatched the locket from Big Baby and smashed it with his cane. Big Baby, now fed up with Lotso's lies and personality, picked him up and tossed him into the dumpster. Then he helped Woody and the gang escape when the garbage truck showed up.
During the credit roll, Big Baby enjoys a happier life at Sunnyside, seemingly adopted by Barbie and Ken.
Big Baby resembles a big toy baby with childlike scribbles that resemble tattoos and a lazy eye. He doesn't speak, but rather gurgles.