Ade Gardner will leave the club to join Warrington Wolves as Head of Performance ahead of the new season.
The former winger, who scored 173 tries in 289 appearances for the Saints, was part of the Academy staff as Strength and Conditioning Coach.
His role also took in the first team on gameday.
“He’s done a great job here and we’re really sad to see him leave,” Saints Chief Executive Mike Rush said. “He will be a big loss to our backroom team but we couldn’t stand in his way.
“This is a big opportunity for him and we all wish him the best.”
At the Saints, Gardner won the 2006 Super League Grand Final as well as the 2007 World Club Challenge.
He also lifted four Challenge Cups in 2004, 2006, 2007 and 2008 and represented both Great Britain and England.