Griffiths has scored 14 goals this campaign after returning to Easter Road from Wolves for a second loan spell, and made his Scotland debut against Luxembourg in November.
Hibs last week said Griffiths would be the subject of a private disciplinary process as police began investigating an alleged racist tweet sent by the 22-year-old.
With his immediate future settled, Griffiths is keen to do his talking on the pitch.
Griffiths, whose Wolves contract expires at the end of the season, told the Edinburgh club's official website: "I've been playing for the team I support and scoring goals to help the club challenge near the top of the table.
"Now the loan deal has been extended I can focus on my football and repay the club and the manager for continuing to show their faith in me."
Hibs also extended the stay of Northern Ireland defender Ryan McGivern, who has made 14 appearances since arriving from Manchester City on loan in August.
The 23-year-old said: "Ever since I moved here to Hibs, I've felt part of the club and I'm really pleased to be able to stay here until the end of the season.
"I've been playing regular first team football which was my main aim, and I believe I've learned a huge amount since August.
"The fans have been brilliant towards me and now I want to help the team build on our encouraging start to the season."
Hibs remain in talks over extending a third loan spell with the future of Honduras midfielder Jorge Claros in the hands of parent club Motagua.
But they tied up a third deal yesterday as second-choice goalkeeper Sean Murdoch extended his contract until May.
