Membrey enjoyed a breakout season in 2016, kicking 44 goals in 17 games.
“The club is delighted to secure Tim for a further two years, which will take him up until the end of 2019,” St Kilda Chief Operating Officer, Ameet Bains, said.
“He obviously had a breakout season this year kicking 44 goals and playing 17 games, which was a reward for his hard work.
“It was obviously disappointing for Tim to undergo a shoulder reconstruction at the end of the 2015 season, but it allowed him to get a lot fitter and as a result his football improved significantly with an improved endurance base.
“At the age of just 22, we still think there is significant room for improvement still left in Tim. So we are delighted that he has locked in with us for at least the next three seasons at the club.”
Membrey has played a total of 29 games for the Saints, since joining the club from Sydney at the end of 2014.