Abigail Marston was a member of Dutch Van Der Linde’s notorious gang of thieves and served as the groups prostitute.
John Marston, another member of Dutch’s gang, impregnated Abigail and in 1895 she gave birth to John “Jack” Marston Jr.
Sometime in 1908, John is left for dead after he is shot when bank robbery goes wrong. John seizes the opportunity to leave the gang and to make a better life for his family. The Marstons buy a plot of land on Beecher’s hope in West Elizabeth and do all they can to create a sustainable family environment. It is unknown when but John proposed to Abigail supposedly “at gunpoint.”
In the year 1911, John is approached by Edgar Ross, a governmental official whose position of power is never explicitly revealed. Ross had Abigail and Jack taken away, and forces John to wipe out his old gang, built up of Javier Escuella, Bill Williamson, and Dutch van der Linde. Oddly while this would arguably be a traumatising event, Jack speaks of it as if it was a mere inconvenience and Abigail says that she was treated fairly well. She claimed that one of the agents "got fresh" with her and that she defended herself and the agent left her alone thenceforth. After John completed the task laid out by Edgar Ross, the family is allowed to return to their farm.
Not long after John's return, Edgar Ross and a small army of his "associates" attack their ranch with the objective of eliminating the entire family. Not long into the battle the family helper Uncle is shot and killed. John is able to get Abigail and Jack over to the barn, putting them on a horse and sending them off, but not before saying his final goodbye. Abigail and Jack ride for awhile but soon Abigail feels the need to go back and check on John. When Abigail and Jack arrive they find John has been shot multiple times, lying in a pool of his own blood. Not long after, they bury him in a shallow grave upon a hill near the farm.
Sometime in 1914, Abigail Marston dies of unknown causes. Jack buried Abigail upon the same hill he buried John near the ranch.
The events of Undead Nightmare are not canonical or exist in an alternate universe of Red Dead Redemption Abigail is infected and turned into a zombie right at the very beginning, after Uncle storms both John and Abigail while they're sleeping. She then bites Jack Marston, and the both of them are tied up in the master bedroom after becoming zombies. She is kept there till the end when John manages to cure the plague. It is shown that both she and Jack died months after, along with John - most likely from the assault Edgar Ross still stubbornly went through with.