The actor - best known for his part as law clerk Jo in the '90s drama - is to make his Albert Square debut later this year, hot on the heels of Alfie's return to the soap in the autumn.
Described as a risk-taker who loves to live dangerously, Michael is more competitive than Alfie and viewers are expected to soon see his manipulative streak as he settles in to life in Walford.
Michael is also a charmer with an eye for the ladies, but he won't think twice before stabbing someone in the back - even those who are closest to him.
Speaking of his casting, Shepherd explained: "I can vividly remember watching the first ever episode of EastEnders and I'm very excited to be joining such a fantastic and iconic programme. Michael Moon will be an exciting character to play - on the surface he's a loveable, cheeky chappy, but underneath he has hidden depths which will be exciting to explore."
EastEnders' executive producer Bryan Kirkwood added: "I've been a fan of Steve John Shepherd's work for years. He's a fantastic signing for EastEnders, an exciting addition to the Moon family, and is set to cause a big splash in Albert Square from the moment he arrives."
Along with This Life, Shepherd has previously appeared in 2004 thriller movie Layer Cake, drama series Waking The Dead and BBC Three sitcom Lunch Monkeys.
> First Look: 'Enders newcomer Michael Moon