De Koning was one of the emerging forces in the Cats' run to this year's flag and was due to come out of contract at the end of the 2023 season.
However, Geelong have stepped in early to ensure rival clubs did not come chasing the 21-year-old's prized signature.
"The club has got a great culture and I want to be part of it," De Koning said.
"It's been a whirlwind 12 months and my focus is to now get back to work, come into training with the same attitude and be hungry to improve.
"I know there's areas I can improve on to take my game to another level and I'm excited to come in every day and work on those things to become the player I know I can be and reach my full potential."
De Koning had played just one AFL game entering the 2022 season but was one of Geelong's most valuable players by the end of the campaign.
He quickly transformed into one of the AFL's best fullbacks, playing on some of the competition's best forwards.
De Koning placed second in the Rising Star award, just behind Collingwood's father-son dynamo Nick Daicos.
To top off an extraordinary season, De Koning booted the first goal of his 24-game career in the dying stages of Geelong's grand final win over the Sydney Swans.
"He played an important role for the team in 2022 and I have no doubt he has the hunger to continue to work on his craft, which is an exciting prospect for all of us at the Geelong Football Club, and for Sam himself,"Â Geelong list boss Andrew Mackie said.
"Sam is a great young man and a popular teammate, and we can't wait to see him continue to grow as a player and person over the next couple of years."
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