"It's taken a little while after the interest in the January window but it's good to finally get it done and concentrate on the rest of the season," Gordon told the club's website (www.celticfc.net).
"It was quite stop-start, there was a lot of things going on within the club, it wasn't a continuous thing. There were two or three occasions when we sat down and talked about it, it was fairly straight forward in the end, I wanted to stay."
Gordon has made more than 100 appearances since joining Celtic on a free transfer in 2014.
Celtic, who have a 27 point cushion at the top of the Scottish Premiership with 11 games remaining, host bitter rivals Rangers on Sunday.
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(Reporting by Shravanth Vijayakumar in Bengaluru; Editing by Angus MacSwan)
