The 24-year old, who was sacked by the Sharks last month following the latest in a long line of incidents, will join the Warriors on a one-year deal.
Seymour says he feels lucky to have the chance to rebuild his career.
“I regret some of the things that have happened in the past but I am desperate to play first grade football again and I want to do everything possible to rebuild my life,” Seymour told Foxsports.
“I don’t want to let them down or let myself down. I know I have to make this work.”
Warriors chief executive Wayne Scurrah said the Seymour’s behaviour would be under close scrutiny at the Auckland-based club.
“Brett knows this is his final chance to make something of his career and his life and together we will be doing all we can to make it work.”