"I knew I could prove that I would compete. Thanks to Tech 3, Yamaha and Michelin, I've done that in two races."
Toseland, 27, won his second World Superbikes championship last season riding for Ten Kate Honda.
"Before this season I had never worked with Yamaha, so for me to gain confidence from the factory in such a short space of time is great," he said.
"For them to show confidence and trust in my ability after just two races is very flattering.
"Signing for 2009 gives me the time to really develop with the team, Yamaha and Michelin.
"I believe that Tech 3 and Yamaha will help me realise my goals of winning races and the championship in MotoGP, and I hope this is the start of a long and successful relationship."