The 28-year-old England international recently admitted that he was thinking about moving to the NRL in Australia.
However, he is now likely to finish his career with the club that he joined in 2004.
"It's great to commit to a long-term deal with St Helens," he told the Saints' official website.
"I signed with them immediately after school and am now entering my testimonial season. It is more than fulfilling to spend my entire career with such a great club."
Roby was part of the England squad that reached the semi-finals of the Rugby League World Cup last month.