Dyer has landed the role of Shirley Carter's brother Mick, who will move to Walford with his family at the end of the year and immediately take over at The Vic.
Kellie Bright is also joining the cast of EastEnders as Mick's wife Linda.
Mick is the youngest of the Carter siblings but although he has always adored his sister Shirley, they have been estranged for years due to animosity between her and Linda.
Billed as a "bloke's bloke", Mick loves his wife, children and dog - and viewers will soon learn that he is a "big softie" at heart.
Speaking of his new role, Dyer commented: "I'm so excited about starting a new chapter in my career and I cannot wait to become part of the East End family."
Linda, meanwhile, has been with Mick since they were teenagers and she has been a barmaid for most of her life.
It's clear to most that Linda wasn't blessed with brains, but beneath her fluffy exterior is a tough woman who will always fight tooth and nail for her family - especially her children.
Bright explained: "I'm very excited about joining the show. Not only am I looking forward to working with Danny, but becoming landlady of The Vic is a real honour."
EastEnders' executive producer Dominic Treadwell-Collins added: "I'm so excited to have actors of Danny and Kellie's calibre joining what is an already strong and talented company of actors. Having been together over 20 years, Mick and Linda have a good marriage and an easy shorthand with each other - but can also still fight like teenagers.
"They will laugh, cry, argue and make up - much to the embarrassment of their children and the delight of Albert Square's residents. Mick and Linda still love each other, no matter what life throws at them. And moving from Watford to Walford, life's about to throw them a few curve balls…"
Dyer began his acting career at the age of 16 when he appeared in Prime Suspect 3 and he has since appeared in a number of film, TV and theatre roles.
Bright's previous credits include parts in The Upper Hand, Ali G Indahouse and Rock and Chips.
The two new signings will begin filming at EastEnders at the end of October and appear on screen at the end of 2013.
As previously announced, Luisa Bradshaw-White has also joined EastEnders as Tina Carter, Shirley's younger sister.
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