Some time prior to the year of 1899, Leon was arrested and transported to the island of Guarma to work on the sugar plantation. He eventually joined the uprising on the island and became a member of the rebel faction led by Hercule Fontaine.
Events of Red Dead Redemption 2
When Arthur and others are captured by soldiers on the island. Leon is seen with some rebels were also captured on the island. When Dutch asks soldiers on who are they and what crime they committed. A soldier states that they are criminals and crime they committed was insurrection.
Leon will sarcastic replies to soldier's comment about rebels being arrested for insurrection and a soldier tells him shut up. The soldiers are eventually ambushed by Hercule's men. Leon is seen bashing a soldier with a rifle and is later seen helping rebel free himself. He is seen fleeing with the others from military reinforcements.
Arthur wakes up tied to a chair in some ruins, and while his captor, Angel, is occupied with Baptiste, he manages to escape from the chair and takes down Angel. Arthur then cuts both Baptiste and Leon free, who had also been captured. Arthur and Leon then venture to rescue some workers scheduled to be hanged, while Baptiste stays back due to his injuries. After saving the workers, Arthur and Leon meet up again with Baptiste.
Red Dead Redemption 2