The actor also scooped up a Golden Globe and BAFTA earlier this year for playing King George VI, but told USA Today that wife Livia Giuggioli has kept him grounded.
"I get more phone messages. That's about it, really. Whatever else you may be asked to do, you can't do all of it," Firth joked.
He added: "You choose the people around you for what you're looking for in certain ways. My wife doesn't take any crap. We go back quite a ways now.
"None of my friends take me particularly seriously. My life is founded fairly solidly in what I have outside this profession. You come back quite dizzy from awards season, and it's quite good to have something solid to come back to."
The actor previously revealed that he remembers very little about his Oscar win.
In November, Firth auctioned off a meet-and-greet session to benefit the Oxfam American charity.
Firth is currently starring in Tinker, Tailor, Soldier, Spy, which is now playing in US cinemas.
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Watch the trailer for Tinker, Tailor, Soldier, Spy below: