All Black signs for Toulon
All Black signs for ToulonSHARE
The four-times capped Mathewson, 31, has agreed a deal that includes an option for a second season in the south of France.
Toulon said on their Twitter account that Mathewson would arrive at the club this week. He will provide competition in an area where Toulon already have options in Eric Escande and Sebastien Tillous-Borde.
Escande is set for a spell on the sidelines after injuring an ankle against Scarlets in the European Champions Cup at the weekend.
Mathewson has played Super Rugby for Western Force, Hurricanes and the Blues, while he had a stint in England last season with Bristol.