Jonah is a young deputy under Marshal Johnson's command in the town of Armadillo. He is portrayed as dim-witted, unkempt, and belligerent. He wears a faded red shirt and black vest along with a bowler hat. He has a strong southern accent, though he insists to be of Irish heritage.
Jonah is first seen by John Marston snoring in a jail cell bed. When Marston tells Jonah that he is from Fort Mercer, Jonah thinks he is a Williamson Gang member and pulls a gun on Marston. An accident is only prevented when Marshal Johnson arrives and calms Jonah down. Throughout the missions Jonah and Marston initially dislike each other but appear to be neutral by the end of the first chapter. Jonah appears to be friends with the other deputy Eli and are often paired up.
His last appearance in the game is Eli and him kicking and spitting on a Williamson Gang member after the battle for Fort Mercer is completed.
It was fast and they died with their bellies full... Well, one of them did.
—John Marston to Marshal Johnson
He appears in the side-mission "Dinner For Two". Marshal Johnson explains that he sent Jonah and Eli out into town, likely to watch over the survivors. Unfortunately, it would seem Eli became infected before turning on Jonah, devouring him.
In the mission "The Assault on Fort Mercer", after cleansing the fort of outlaws and regrouping with Marshal Johnson, Jonah can be seen doing the same tricks with his revolver that the player's character does after being the top scorer in a competitive match.
In the mission, "Justice in Pike's Basin", the player has a choice to follow Leigh Johnson or Jonah and Eli. If the player chooses to follow the deputies, Jonah appears more friendly to John. He is also heard shouting "Marston got one!".
Despite his skinny frame, he is very strong, able to carry a tied up Norman Deek on his shoulder with no problem.