Brown, who has been in charge of the Knights since taking over from Rick Stone at the start of 2016, has helped the club rise up the ladder this season and they are pushing for a return to the playoffs for the first time since 2013.
This contract is unusual in that it is entirely performance based.
Knights CEO Philip Gardner said he was confident Brown had set the club up for a successful and sustainable future.
“Nathan is comfortable with the contract, the terms of which demonstrates the confidence and trust that the club has in Nathan and vice versa,” Gardner said.
“Nathan is a top-ranking coach from both a development and high-performance prospective. We have seen clear improvement this season and have high but realistic expectations for season 2019 and beyond.
“Nathan’s vision has never waived and he has shown the patience and resilience needed to develop a successful program at the Knights.”