Isabella of Majorca is the daughter of James III and his first wife, Constance of Aragon.

Her maternal grandparents are Alfonso IV of Aragon and his first wife Teresa d'Entença.

Her paternal grandparents are Ferdinand of Majorca and his wife Isabelle de Sabran.

After the death of her mother, Isabella's father had remarried to Violante of Vilaragut, who gave Isabella a half-sister named Esclaramunda, who died young.

Her father had lost the kingdom of Majorca in 1343 and died two years later in the Battle of Llucmajor fighting against the forces of Peter IV of Aragon.

Isabella had been captured with her brother and stepmother by her uncle King Peter after the battle in which her father was killed, and confined to the convent of the Clarissans at Valencia with her stepmother.

She is freed in late 1358, thanks to the efforts of her stepmother, on the condition that she renounce her rights to Majorca.

On September 4, 1358, Isabella marries John II, Marquess of Montferrat, in Montpellier.

Her marriage is arranged by her stepmother, who is at this time living at the Court of Monferrato.