She was born in 1248, the only daughter of Manfred of Sicily and his first wife Beatrice of Savoy. More important, her paternal grandparents were Frederick II, Holy Roman Emperor and his mistress Bianca Lancia. One of the most important, in view of its future consequences, was the marriage between James I's son Peter and Constance at Montpellier on June 13, 1262. As Manfred was at war with Charles of Anjou and the papal party, the Pope naturally regarded this as a very unholy alliance. He attempted to scuttle the marriage by urging Louis IX to break off the proposed match between his son Philip and James's daughter Isabella. However, political considerations and James I's promise not to help Manfred overcame the French King's scruples and the French marriage took place in July 1262, a month after the alliance with Manfred had been celebrated at Montpellier.
With the death of her parents in 1266, the mother of Roger of Lauria became her foster mother. Beatrice had been her wet nurse and had followed her with Roger to Aragon. She would have a close relationship with Roger for the rest of her life. She was influential in bringing into the court John of Procida and other refugees, such as the Lancias. There is little doubt she was highly involved in the intrigues to undermine Charles of Anjou and as a Hohenstaufen she brought immediate legitimacy to the claims of Peter III. She would have six children with Peter III: Alfonso III, James II, Elizabeth of Aragon (married Denis of Portugal), Frederick III of Sicily, Yolanda of Aragon (married Robert of Naples), Infante Pedro.
She followed Peter to Sicily and ruled in his sted when he was forced to return to Aragon in October 1283. When Charles of Salerno was brought to Messina following his capture at the Battle of Naples, it was her direct intervention which prevented the city mob from lynching Charles on the spot. She was committed to the Sicilian cause and sold off part of her personal belongings to help fund the fleet in 1283. Even after Peter's death, she continued to have considerable influence at the Sicilian court. An example of this was an incident in 1291 when Roger of Lauria captured a Florentine ship hired by the papacy to take supplies to Acre. Instead to writing to James of Sicily to plead for its release, the pope wrote to Constance to have her plead with Roger to free the ship. After leaving Sicily with Roger of Lauria in 1295 following the Treaty of Anagni, she became a nun and died at Barcelona in 1302.
