The 26-year-old Kiwis international said he was thrilled to settle his future with the club in what he regards as the most important contract of his career so far.
"This was a big contract for a lot of reasons and I'm excited to be able to lock it away and know I'll be here for another two years," he said.
"My belief in this club is massive and my belief that we can do something special here is bigger than ever with everything we have in place.
"I have always said in the past that I could never imagine myself being anywhere else but the Vodafone Warriors. I'm that kid who came up through the system and I love it here and what the club has done for me. There was more to think about this time but, in the end, it came down to winning.
"I could go to another club and another system but I realised winning there [at another club] wouldn't mean as much as winning here. That's what I want to be a part of here."
Johnson's two-year contract leaves him in line to extend his career to nine seasons with the Warriors.
