The Oscar-winning actress began dating Toth in January, shortly after she split from Jake Gyllenhaal, and went public with their relationship in March.
Us Magazine reports that Witherspoon's rep said the pair are "extremely happy", and that Witherspoon's children Ava and Deacon also "are happy with him".
Toth works as an agent at the Creative Artists Agency, where Witherspoon is a client, though Toth does not directly represent the How Do You Know actress.
A friend of Witherspoon told the magazine: "She is definitely happy, in love and definitely wants to settle down."
The blonde star had recently joked about engagement to Entertainment Weekly, saying: "My mum always texts me, like, 'Are you getting married?'
"I'm like, 'Mum, come on! You would know if I was getting married.'"
Witherspoon was previously married to actor Ryan Phillippe for seven years until their divorce in 2008.