Currently in his first season as captain, the 29-year-old has played 161 games for St Kilda since being selected with pick 57 in the 2007 AFL Rookie Draft.
Geary said he was committed to helping accelerate the development in the playing group and leading the club’s return to finals action.
“We have shown at different stages this season that our best stacks up against any side but we haven’t been able to produce the level of consistency that we are working so hard to achieve,” Geary said.
“No one is content with the position we find ourselves in and we are desperate to finish the year off strongly.”
“It’s been an unpredictable season to date and all we can do is get to work this week and perform strongly in our remaining games.”
“I see a huge amount of upside in this group and I’m thrilled to be extending my contract by a further year to contribute to our continued development.”
St Kilda Chief Operating Officer Ameet Bains said Geary’s influence on the group was significant.
“Jarryn has been an important leader at the club for many years but has really grown in the captaincy role this year,” Bains said.
“He is enormously respected by his teammates and coaches alike for his selfless attitude, and someone who really sets the benchmark for professionalism on and off the field.
“He has continued to perform at a really high level this season and is an integral part of our defensive unit. We are really pleased to have secured his services until the end of 2019.”