Guillaume de Launcet was the eldest son of Comte Reynaud de Launcet, a minor Orlesian noble. As a child Guillaume was betrothed to Leandra Amell. The next summer Guillaume met Leandra for the first time at his father's country estate.
Several years after their betrothal, Leandra fell in love with Malcolm Hawke, a mage, and fell pregnant with his child. Her brother attempted to convince her to pass the baby off as Guillaume's. When Leandra went to break off her relationship with Malcolm, he used the opportunity to propose. Leandra accepted Malcolm's proposal and left for Fereldan with her fiance.
Sometime after Leandra broke off their engagement, Guillaume met and married a woman named Dulci with whom he had several children. One of their children, Emile was discovered to be a mage at the age of six, and was taken to the Kirkwall Circle of Magi.
Guillaume is involved in the quest On The Loose.After Knight-Commander Meredith asks Hawke to retrieve three magi who have escaped the Circle, Hawke will go to the de Launcet manor in Hightown. There, Hawke will talk to Dulci about Emile. Guillaume will burst into the room and begin a rant about how much trouble his son is causing. Dulci will then reveal that she gave Emile some money to leave Kirkwall and begin a new life. Hawke must then go to The Hanged Man Tavern and talk to Emile. Emile can be turned in to the Templars or allowed to leave in order to start his new life outside of Kirkwall. If Emile is allowed to leave, Dulci will send Hawke a thank you letter along with some gold. If Emile returns to the Circle and is allowed to sleep with a tavern girl named Nella, the latter will come to the de Launcet manor, claiming to be pregnant with his child; Guillaume will comment that he should hide her on the country estate.