Tess is the first child of Claude Dombegh and his second wife, Anne-Marie Dombegh, although her father has an older daughter from his first marriage. Tess often misbehaved as a child, and her parents and family tended to treat her poorly as a result. Tess and her twin sister, Jeanne, were very close growing up, although they gradually grew apart as Tess began to spend more and more time with her boyfriend, William of Affle. Tess and Will shared a love of science and quigutl folklore, which spoke of World Serpents--giant serpents that supposedly lived under the world, including Anathuthia, whom she learned about from her quigutl friend, Pathka. However, William raped, impregnated, and abandoned Tess, and she gave birth a few months later to a baby who died a few days after being born due to his premature birth. This was considered a huge scandal, and Tess could no longer be married off as was planned. Because the two sisters needed to be married in order, their father legally changed the order of their birth, making it appear as though Jeanne were the older twin.
Two years later, on Jeanne's wedding night, Tess was involved in a fight with Jeanne's brother-in-law Jacomo due to disagreements between the two as well as her own personal struggle with the roles that she and Jeanne had been forced to play as women, especially relating to sexual expectations for them. She decided to take Jacomo's name, disguise herself as a man, and go on the road to look for Anathuthia, which is the main plot of Tess of the Road.
Tess is often rash and reckless, and she has a severe drinking problem, probably caused by many factors from her childhood and adolescence, including having been treated poorly by her parents and family and having been abandoned by William, thus destroying her social standing, her reputation, and, in many ways, her life. However, she is very loving, especially toward her sister and closest friend, Jeanne. She is also inherently curious, which has led to her getting in trouble in many situations.
Tess met William of Affle at an astronomy lectured that she attended with Kenneth, her mother's much younger brother, whom she considers to be a cousin. Kenneth was distracted by a young man named Lord Rynald, with whom he developed a possibly-romantic relationship, and Tess began to spend more time with William under the pretense of spending time with Kenneth. Their relationship became romantic, and he ended up raping her while she was drunk and unable to consent. She continued her relationship with him in the hope that he would marry her, thus removing the scandal of her loss of virginity, but he abandoned her shortly before she found out that she was pregnant. Throughout the book, her memories of William continue to haunt her, and it isn't until she reaches Affle (or Afale), his hometown, that she is able to fully come to terms with the memory of their relationship and her pregnancy.
In Tess of the Road, Tess begins a relationship with Josquin, who had previously appeared in Shadow Scale as part of the Ninysh guard that escorted Seraphina and company through Segosh and the surrounding areas. Although he was about ten years older than her, they were on very equal footing in their relationship, and though they had (consensual) sex, there was more to their relationship than that. Ultimately, the two ended their relationship amicably when Tess left to continue her journey.
Tess and Pathka are close friends. They met when Tess was very young, and she helped Pathka lay an egg that was going to kill him. They reunited in Tess of the Road and together, they went in search of the World Serpents.
Tess and Jeanne are fraternal twins, and they have always been very close, saying that it was "us against the world." However, by the end of Tess of the Road, they are no longer on speaking terms. Jeanne feels betrayed that Tess refuses to come back to Goredd, and she tells Tess over thnik that she hopes she drowns.