Pybus, 19, was released by the Black Cats without making a senior appearance, but was part of this season's Football League Trophy squad.
He had been training with the Bantams and played for the reserves.
"Having trained with the lads already, I feel more confident now around the club," Pybus told the club website.
Bradford City have signed free-agent midfielder Daniel Pybus on undisclosed terms, following his exit from Sunderland at the end of January.