Savage, 19, showed no emotion as the verdict was read. He now faces a sentence of life in prison without possibility of parole, prosecutors said.
Kimmie, who functioned at the level of a 9-year-old due to a disability since birth, disappeared Aug. 17, 2010 after leaving her home to ride her bike to a friend's home.
Savage was an acquaintance of Kimmie, and the two met at a spot near her home. Prosecutors said Savage coaxed the 16-year old into the brush and when she asked to leave, he choked her to death.
The prosecution based its case on Savage's taped confession the day he was arrested. It was played again for jurors on Monday.
"She got up and started to go and I just choked her from behind," Savage said on tape the day he was arrested. "She died and I threw her in the sticker bushes kind of afraid of what I did."
Deputy Pierce County prosecutor Phil Sorensen then demonstrated the choke hold to the jury.
"So he subdued her. He got up and he threw an arm around her neck and he held her until she went to the ground," Sorensen said.
Savage's defense team had painted a different picture of their client, claiming the death was an accident during rough sex at her insistence.
"She told me she wanted me to tie something around her neck," Savage said during his testimony.
He told the jury he felt uncomfortable about the request, but went ahead with it anyway.
Instead of premeditated murder and rape, Savage defense attorney Les Tolzin told the judge during trial his client should only be convicted of second degree manslaughter, admitting Savage should have known what he was doing could lead to death.
Savage will be sentenced on Jan. 17.