He has been speaking out after a report by the Equality and Human Rights Commission showed many Christians were fearful of speaking about their beliefs at work.
Writing in the Telegraph, Lord Carey said: "Now, more than ever, we need Christian people to speak up for their faith, to articulate their beliefs in sensible and courteous ways. Our society needs a reminder of our foundational beliefs in honesty, faithfulness, right and wrong.
"Don't be intimidated by a hostile workplace, challenge the hostility with good humour."
The report discovered widespread confusion over the legislation and many Christians reported that they feared their religion is losing its place in the workplace and in society more generally.
"A recurring theme among some employees was the pressure they felt they were under to keep their religion hidden at work and feeling discriminated against when it came to wearing religious symbols or expressing their beliefs," the report found.
It added: "People reported being mocked for their beliefs including Christians, who said their colleagues assumed they were bigoted."