Leeds believed they had all but secured his signature after agreeing terms with him.
Chief Executive Shaun Harvey said on the club's website: "Terms were agreed with the player for him to join Leeds, subject only to him passing a medical.
"The player has since reneged on the agreement reached and joined Newcastle United. We are, both disappointed and relieved, as we would have very much liked Olivier Bernard to strengthen our squad.
"But if he did not want to play for Leeds United it is better to find out now, as we are only interested in players who are fully committed to the club."
Bernard left Tyneside in January last year to join Southampton on loan and made a move to Ibrox a year ago.