McStay, who has played 52 games with the Lions, with now remain with the club until the end of the 2019 season.
“We’re really pleased to have Dan re-sign with the Club,” Lions general manager of football, David Noble said.
“We see Dan as a long-term player for us and believe he has a strong part to play in our future.
“This re-signing is another indication of our players buying into our Club.
“To have Dan join a number of our guys in re-committing to the Lions already this year is important for both the present and the future of our Club.”
McStay joined the Lions with the No.25 pick in the 2013 National Draft. The 22-year-old has averaged 10.6 disposals and 3.8 marks per game this season