The Business star will play Mick Carter, the new landlord of the programme's iconic Queen Victoria pub, when he joins in December (13).
He says, "I'm so excited about starting a new chapter in my career. I cannot wait to become part of the East End family."
The move onto the small screen comes after Dyer, who grew up in London's East End, originally turned down an offer to star in the show in 2009.
After meeting with a Bbc controller, he explained, "I quite like the idea of it. But actually, in reality, I just got cold feet. Just from having a meeting it's all over the newspapers and it gave me the horrors. Imagine if I went in it.
"With the EastEnders thing the whole publicity gets out of hand. It's like a whole new beast. It's not something I fancy. I don't want to write if off totally but at this point in my career I think it would be madness."