He joins fellow All Blacks Luke McAlister, Malakai Fekitoa and Ma'a Nonu at the French Top 14 club.
It's Mathewson's latest stop in a career which has taken him from the Hurricanes to the Blues to the Western Force and domestic stints with Wellington, Hawke's Bay and Canterbury.
He had a stint in England last season with Bristol, but has most recently been plying his trade with King Country in the Heartland Championship.
The 31-year-old, who played four tests for the All Blacks, 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.
Meanwhile the Wellington first-five Jackson Garden-Bachop has signed a two-year deal with the Hurricanes.
The 23-year-old joins the franchise having made his Super Rugby debut for the Melbourne Rebels this year.