Syed is the much talked about son of Masood Ahmed (Nitin Ganatra) and Zainab Masood (Nina Wadia).
Elliott's character will apparently be a smooth-talking natural charmer who knows how to get ahead in business. He is also described as "handsome, suave and sophisticated".
"At last he's here! The most talked-about yet unseen prodigal son in EastEnders history," said exec producer Diederick Santer.
"Syed is a fascinating character, and I'm sure Marc will bring his many dimensions to life with great verve. Entrepreneurial, reckless, dashing and complicated, he's set to bring surprises and chaos to the Masood family."
Speaking about his arrival in the square, Elliott said: "It is so exciting to join the cast of EastEnders and to be working with actors such as Nina Wadia and Nitin Ganatra who I have admired for many years.
"The Masood family have really made a name for themselves in the Square and it will be interesting see how Syed plans to stir things up!"
Elliott's credits include Holby City, The Bill and the History Boys UK theatre tour.