The network said the show will wrap up with nine episodes in the summer of 2010.
The series has been averaging 3.5 million viewers going into Tuesday's second season finale.
"Since 'Saving Grace' began in 2007, the series has both challenged and entertained viewers in ways few other shows on television ever dare," Michael Wright, an executive vice president who heads up programming for TNT, TBS and Turner Classic Movies, said in a statement. "The show's continued success is thanks to the amazing talents of Holly Hunter and Nancy Miller, along with a tremendous ensemble cast and a highly skilled production team. They have taken us on a unique journey, and we look forward to seeing where it will ultimately lead."