Sibylla had very little personal power, but was instead a pawn in the political alliances in the Kingdom of Jerusalem. Raymond III of Tripoli, who acted as regent for Baldwin IV while Baldwin was still underaged, arranged for Sibylla to marry William of Montferrat in 1177. However, William died later that year, while Sibylla was pregnant with the future Baldwin V. After William's death representatives from Flanders suggested she marry a minor noble from their county, and in 1179 Baldwin of Ramleh, head of the powerful Ibelin family, offered to marry her. However, in 1180 Baldwin IV had Sibylla marry Guy of Lusignan, a newcomer to the kingdom. As this caused Baldwin to lose much of his support among the older families, he tried to divorce Guy and Sibylla in 1184, but Guy was by now trying to take control of the kingdom. In an attempt to undo Guy's influence, Raymond III took over the regency for Baldwin IV, who was now incapacitated with leprosy, and promised that if Baldwin V while still underaged he would form a committee to decide who had the best claim to the throne, Sibylla or her sister Isabella (or, more accurately, which of their husbands would claim the throne in their name).
Baldwin V did indeed die as a child in 1186. Sibylla, Guy, and Raynald of Chatillon, rather than waiting for the formation of Raymond's committee, managed to take control of the throne. Many of the nobles were opposed to this, and at Sibylla's coronation they demanded Sibylla divorce Guy. She agreed to do so, on the condition that she would be allowed to choose a new husband, and she immediately re-married Guy, to the dismay of the nobles who had not considered this possibility. Sibylla remained queen, with Guy technically her consort, although he held all the real power.
Guy was captured during the Battle of Hattin on July 4, 1187, and Sibylla led the defense of Jerusalem during Saladin's siege in September. The city eventually fell to Saladin on October 2. Sibylla escaped to Acre, but she and her daughters died there in 1190 during Saladin's lengthy (and ultimately unsuccessful) siege. As Guy was only officially Sibylla's consort, the crown, now only nominal, passed to Isabella and her second husband Conrad of Montferrat.