Lynch is in his second spell at the Jungle, after he rejoined from Hull FC in 2014.
The player is delighted to be staying on until the end of the 2016 season.
“I am really pleased to have extended my stay here for another 12 months at least,” he said.
“I am happy with the way my rugby is going, so it was a simple decision.
“The club have helped me out with my testimonial in the past year, and it just shows what a good club it is to be a part of.
“I am looking forward to linking up with the new players, and we have showed some good signs in the two friendly games so far.
“I think there is lots of quality in the squad this year, and I do not see why we cannot have another strong campaign.”