How long had Marley been dead in A Christmas Carol?

Marley has been dead for seven years.

When the story begins, Scrooge is asked about his partner Marley by the men collecting money for charity.  Scrooge’s counting house is still named “Scrooge and Marley.”  He even answers to both names.  When the men ask about his partner, Scrooge tells them that he is dead.

“Mr. Marley has been dead these seven years,” Scrooge replied. “He died seven years ago, this very night.” (Stave 1)

Although...

Marley has been dead for seven years.

When the story begins, Scrooge is asked about his partner Marley by the men collecting money for charity.  Scrooge’s counting house is still named “Scrooge and Marley.”  He even answers to both names.  When the men ask about his partner, Scrooge tells them that he is dead.

“Mr. Marley has been dead these seven years,” Scrooge replied. “He died seven years ago, this very night.” (Stave 1)

Although Marley’s death might be a reason to not like Christmas, since his dying on Christmas Eve might bring back bad memories to associate with the holiday, that is clearly not so.  Scrooge was bitter and lonely even before his partner died.  When he is visiting the past, the Ghost of Christmas Past shows him the Christmas Eve that Marley died.

“…I passed his office window; and as it was not shut up, and he had a candle inside, I could scarcely help seeing him. His partner lies upon the point of death, I hear; and there he sat alone. Quite alone in the world, I do believe.” (Stave 2)

The fact that Scrooge would not sit with his partner as he was dying, and decided to work instead, shows that he did not think much of other people even then.  Marley was the person that mattered most to him in the world, and he was not there for him.  When Marley’s ghost appears to Scrooge, Scrooge is happy to see him, once he gets over the shock.  He tells Marley that he was always a good friend.

Marley became a ghost, and watched over his friend Scrooge even in death.  He decided that he could not stand back and watch Scrooge commit the same mistakes he did.  He was unable to rest in death, watching the poor and suffering and not being able to help them.  So he decided to help them through Scrooge.  First he helped Scrooge see the error of his ways, and then Scrooge made it his business to celebrate Christmas by helping others.