Marcel Dumas is a business owner and a Creole street gang leader in New Orleans. In season 5 Teresa helped plan his escape, however she gave him into the police instead of Boaz who killed Judge Lafayette. He was arrested for the murder of 'The Judge' and his son, however he was innocent. Teresa ensured his release from prison and later left him funds to complete the Water front property to become a legitimate businessman.
Marcel Dumas runs a crime syndicate in NOLA and when Teresa's bar opens, he goes to welcome her to the People of Color Chamber of Commerce, while his intention is to gather information on the new player in town. Marcel is shown to take guidance from his step father Lucien, and to observe respectful relations with the corrupt Judge Lafayette.
When Javier and Boaz disappear, Teresa and her team falsely assume Bobby, who works for Dumas has anything to do with the situation and kidnap him. Bobby dies of an accident on Teresa's watch. Dumas takes revenge by killing Birdie until Teresa pays the Judge to put an end to the war with Dumas.
Teresa starts selling coke to Dumas and his gang makes a lot of money. As Teresa is unable to get under the Judge's skin, who is adamantly looking for the murderer of his nephew Renee, Teresa targets Dumas to become her associate. She wins Dumas over by exposing to him his man Cedric who snitches to detective Green and the Judge. She proves to him that the Judge is their common enemy and Dumas sides with her against Lucien's advice.
When the son of the Judge commits suicide, the Judge blames Dumas and he becomes target for law enforcement. Teresa sends James to smuggle him out of state, however Dumas stops to see Lucien who betrays him and James and Dumas end up being chased by the police. James ditches the pursuit and hides them in a safehouse where he is able to convince Dumas that Teresa did not order the hit on the Judge and that she is on his side.
Teresa is forced to hand in someone to the police and as she cannot hand in Boaz due to his crucial importance to her Mexican operation, she hands in Dumas. Both James and Dumas are shocked. Teresa makes plans and does everything possible to find a lawyer for Dumas and to free him. Dumas refuses to buy coke from her and has difficulty believing that Lucien is the snitch.
Teresa frees up Dumas from jail later in the last season but he still refuses to do business with her. He kicks her and James out as he considered her family and she betrayed him. Dumas has to kill a young man who is insubordinate and determines for himself that the life as a crime boss is not what he wants to pursue. Dumas gives his biz to Cedric.
On the finale Dumas refuses to work with Boaz who has taken Teresa's place. He helps Pote get his revenge on Boaz. Before disappearing Pote gives Dumas the ownership to the waterfront property and the funds to complete the project that Teresa has left for him. Pote tells Dumas that Teresa always considered him a friend.