The actor, who plays Carson the butler in the period drama, speaks out against cutbacks to health services for youngsters with hearing problems in a public service announcement for Britain's National Deaf Children Society.
Carter is urging fans to add their signatures to the Stolen Futures petition, which he hopes will make politicians reconsider the cuts.
He says, ""Every day cuts are being made to services to deaf children. By services I mean teachers of the deaf, speech and language therapists - people that deaf people rely on for their education. We want to take down the barriers and give them opportunities, let them realise their potential. That's what every parent wants for their child.
""I would like to ask you to sign our petition today to protect the future of thousands of deaf children.""
British actress Scarlett Alice Johnson has also added her support, insisting, ""These services are not a luxury, they are vital to the education, health and wellbeing of deaf children.""