Williams has re-signed with New Zealand Rugby, the Crusaders and Canterbury Rugby through to the end of 2029.
The 2027 men's Rugby World Cup is in Australia, while the British and Irish Lions will tour Aotearoa in 2029.
Williams now holds the longest current Crusaders contract.
"The Crusaders means a lot to me. I'm excited for this opportunity and I feel like Christchurch is the best place to be," Williams said.
The 25-year-old first entered the Crusaders environment at the end of 2018 when he was selected for the Crusaders Academy out of school.
He went on to become the youngest member of the Māori All Blacks in 2020 and made his Crusaders debut in 2021.
The 24-year-old made his All Blacks debut in 2023, playing at the World Cup that year. He has 18 Test caps.
"Watching the Crusaders for a few years - you aspire to be in the jersey, and you think about all the people who have worn it before you. To get to put it on every week is a privilege," Williams said.
"The character of this place and the people inside those four walls - not only the players but everyone involved in the franchise is what makes it special."
Williams is looking forward to playing with the Crusaders at Christchurch's new Te Kaha Stadium, which opens next April.
"Christchurch deserves it. It has been through so much over the last few years and a lot of success has come out of this place but not by accident and I'm blessed to be able to play a little part here for the next few years. I can't wait to just keep giving myself to this place."
Crusaders head coach Rob Penney said Williams has already created a legacy at the franchise.
"Having him sign through to 2029 and for the Crusaders to watch what should be the best part of his career unfold will be a great privilege.
"His world class performances on the field are obvious for everyone to see, but what might not be so obvious, is a big hearted, generous, and caring family man we get to see every day off the field. That is a critical part to the Crusaders culture and his influence in that area will be ongoing."
