Gilliead recently returned to Newcastle from a loan spell at League Two club Luton, where he scored two goals in 21 games in all competitions.
The 20-year-old, who has yet to make a first-team appearance for the Magpies, spent last season on loan at Carlisle.
He is Bradford's second signing of the transfer window, following the arrival of Birmingham striker Alex Jones.
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League One side Bradford have signed Newcastle midfielder Alex Gilliead on loan until the end of the season.