The 51-year-old - who is married to Italian film producer-director Livia Giuggioli - said people are often dismissed as being vacuous and stupid by others just as much as they are celebrated for their attractiveness.
"There was a time when a beautiful person was considered something fine and to be celebrated. Now a beautiful person is assumed to be shallow and flaky. If you are beautiful in today's society, you are presumed to have no substance.
"I think a lot of talented and very bright people who are also physically beautiful have to work very hard if they don't want to just lean on their looks," Firth said.
Despite his incredible success, the actor also said his parents are not particularly impressed by his career choice.
"I think they quite like it when I play a role that they consider to be rather worthy of the profession, a role where calling yourself an actor isn't an apology.
"It will inevitably be something Shakespearean that they consider superior. When I just prance around in 'Mamma Mia!', or something like that, I'm not sure how they reconcile themselves with the son they produced."
'The King's Speech' star's father David was a history lecturer, while his mother Shirley is a religious academic.