The Edinburgh outfit have been buoyed by the form of Manchester City defender McGivern and Wolves striker Griffiths (14 goals) so far this season and manager Pat Fenlon was thrilled to be able to keep both players on his squad for the remainder of the campaign.
"We are delighted to be able to keep both players until the end of the season," Fenlon told the club's official website.
"Both Leigh and Ryan have made massive contributions to the team and have been good for us.
"We've already said that we would do everything we could to keep them at Hibernian and fortunately all that hard work has come to fruition.
"This news gives everybody connected to the club a boost as we return after the winter break for Saturday's home game against Dundee."