The 25-year-old Scotland striker signed for the Scottish champions from Wolves in January 2014.
Griffiths will speak to the media at a hastily-arranged press conference at Celtic Park on Friday afternoon.
Griffiths, who is Celtic's top scorer this season with 19 goals, is relishing the prospect of at least five more years in a green and white jersey.
He told the club's official website: "I love putting the Celtic top on every time and feeling that expectation to win every week.
"I'm looking forward to the next five years in the Hoops as we look to add to the trophies already won."
Source : PA
Source: PA