The Oscar-winning actress, 34, and Toth, 40, began quietly dating last January and quickly grew serious about each other.
In October, a source close to Toth, an agent at Creative Artists Agency in Los Angeles, told PEOPLE he was smitten with Witherspoon.
"Jim knows Reese is the one for him," the source said. "It's what he's been waiting for. [Getting engaged] is a natural step for them."
Witherspoon was equally thrilled with the relationship, a source close to the actress told PEOPLE at the time. "Reese quickly realized that Jim was someone that she felt safe with and could count on," the source said.
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