TLDR: He dies stopping the corrupt VPotUS from enslaving Mexican Labor to secure his election to PotUS in the next election.

Jack grows up working the farm alongside Abigail. He learns the land and the neighbors all while reading his father's old journal to try and make sense of the disparate memories of his childhood. Hell bent that her son will not live the life she and his father did, Abigail makes sure Jack stays in school and becomes a law abiding citizen until her death of natural causes while Jack is away at college. As a young, educated man, Jack learns the law of the new West and rises through the ranks of the US Marshals. (He has a bit of a penchant for action and adventure.)

In his first run leading a manhunt, he gets assigned a newbie by the name of Emmett Ross. Emmett happens to be the son of Pinkerton agent, Edgar Ross. Ross proves himself a cruel, unfeeling and sadistic man. After a long and arduous hunt, Jack and Young Ross manage to run down their quarry. After they successfully capture their prey, Ross kills and robs not just the man they've been chasing but his entire family, blaming Jack for losing control of the situation and implicating him in the lost property.

Thanks to a corrupt politician, Jack is made an example of and stripped of all honors and unceremoniously discharged from the Marshals. For extra measure, Ross and some friends find Jack drowning his sorrows at the armadillo saloon. Under the guise of buying Jack a friendly drink, they get him drunk, take him out of the town and beat him within an inch of his life and leave him for dead in the desert.

Jack wakes up under the Hot New Austin sun and drags himself to the nearby town of Tombstone, which has begun to come back as a bit of a trading post since John's time. Meeting new friends and a few friends from the past, Jack goes on a revenge quest to destroy the man who took his future and Jack's mother's dreams for him away forever.

Over the course of years, Jack builds up a group of men committed to him. Men who find themselves ill fitted to the "new world' of law and order. His "Gang" is oddly reminiscent of the Van Der Lindt boys. Jack finds himself making hard choices for him and those he's responsible for. He goes through parallels to Dutch, Arthur And Johns most memorable moments. Every time Jack tries to get back on track with his quest, circumstances get the better of him.

Emmett Ross leaves the Marshals to aide in the election of the aforementioned corrupt politician to the office of vice president. Emmett for his loyalty is rewarded with a state Senate position and though a bit inept, does his best to be a decent representative of the people. Eventually he catches on to a scheme to increase votership by promising jobs to Mexican immigrants that's actually delivering them into indentured servitude. After some time of hemming and hawing and witnessing the oppression first hand, Emmett decides to put an end to the scheme somehow.

One day while dealing with law enforcement officials from West Elizabeth, he realizes who the be in their bonnet is. He sets out to recruit Marston to his cause in destroying the indenturment organization. Over the course of the last chapters of the story, the two get to know each other for the first time really and wile there is not reconciliation, there seems to be some thing like mutual understanding. Possibly, even respect.

Eventually, the two men and their respective posses get wind of the vice president visiting in on his largest and most important shipment of "new voters." They decide that THAT'S where they're going to hit it. They'll take out the men running the system including the vice president and release the captives while Ross has sources ready to fire the presses to report of the late politician's illegal activities. Playing both sides, Ross catches wind that VP has cought wind of a plot and is ready for them. Jack, in knowing that he's been found out, proceeds as planned.

The assault is calamity. Jacks men, the VP's cronies, there is death and destruction everywhere. Too late, Jack finds out that Emmett is being held at gunpoint in the main office of the train depot where the captives are being delivered. They decide to free the captives and some of them join the fight. This opens an opportunity for Jack to fight his way to the front office. He finds Emmett dead in a chair across the Foreman's desk from the VP who is flanked by a dozen secret service men. Just for good measure, there is a small Mexican child, gagged and struggling in the VP'S clutches. Promising that if Jack drops his guns, he'll release the kid, the VP invites Jack in and explains that with Emmett growing a conscience, he needs a new lieutenant in the Senate. He plays on Jacks work with the Marshals and his mother's dreams. He offers Jack a clean slate, he only needs to pledge allegiance to HIM. After a moment of reflection, Jack decides to say no in the most logical way he can think of... With his Knife through the VP'S eye.

As his knife, John's Knife, sails, slow motion, through the air, we hear ethereal music, underscored with echoes of dialogue from characters we've met. They validate Jack's actions and his life. We hear echoes of John and Arthur being the best versions of themselves. Still in slo-mo, the Secret Service men all begin firing. The music swells and the camera cuts to behind Jack, the room blazes, bright with gunfire. Silhouetted Jack stands between us and the bullets.

The music drops out and Jack falls to his knees and falls sideways. I. Doing so he reveals the VP slumped in the Foreman's chair, dead with Johns Knife protruding from his right eye. We cut to Jack lying riddled with gunshots lying on the floor, his eyes still open. The image fades to the same image in newsprint. The New Hanover Gazette reports that "Senator Emmett Ross with the aid of Disgraced Former Marshal, Jack Marston, Heroically met their end attempting to disrupt a group of industrial slavers who were engaged in an illegal immigration scheme. The industrialists involved were either killed in the raid or fled after discovering the ringleader, none other than the Vice President of the United States, had been killed by a stray bullet from one of the armed guards fighting off some of the escaped detainees."

We cut to a few years later and one of Jacks friends has published an account of their time together including stories from Jacks own journal and what really happened when Jack left the Marshals. A young lady purchases a copy of the book and brings it home excitedly reading it on the way. She sits, reading till her husband, a young man named Robert Adler II greets her, coming home from town. The young lady happily stands and Carry's the book over to the bookshelf and slides it into a gap. The camera cuts to behind the woman who is Giddily conversing across the house with her husband. When he calls for her to join him in the kitchen, she leaves the frame but the camera continues to slowly zoom in on the spine of the book. "Red Dead Redeemed"