Laurel doesn't get along well with her family. It's also implied that her father wasn't a good person and probably negatively influenced her. She is Latina and bilingual, primarily speaking Spanish with her family.
Laurel Castillo first speaks up on her first day of Law School when she interrupts a one on one conversation between Wes Gibbins and Annalise Keating. Annalise is trying to help Wes answer a question, but Laurel shouts out the answer before he can get it. She's scolded for taking a learning opportunity away from him. Laurel and the rest of the students are then taken to see Gina Sadowski, a client Annalise is trying to help. She asks the students to come up with a defence for the woman as a competition. Laurel gets straight onto the task and when she reveals her idea, she makes it through to the next part of the challenge. She begins attending the court sessions and witnesses the impressive rivalry between Connor Walsh and Michaela Pratt. After one court session, Laurel goes to the rest room and sees Gina stood in front of the mirror. She goes into one of the cubicles and spies on her, seeing her get comforted by the wife of the man she apparently tried to kill...implying they're in cahoots and she's in fact guilty. Laurel reveals this to Frank Delfino, but he explains that he already knew before making some misogynistic comments. Laurel is angry that these lawyers are so immoral and would let a guilty woman walk free. After the trial is over and Gina is found not guilty thanks to Nate Lahey, Annalise's boyfriend, Laurel observes more friendly behaviour between Gina and the other woman. Back at the university, Annalise reveals that Laurel is one of the students who won the competition, but a smile from Frank implies that he influenced the choice. 
After the unfortunate murder of Annalise's husband, Sam Keating, Laurel, Michaela, Connor and Wes flee to the woods near the university in a panic and to decide their next plan of action. Wes brings with him the murder weapon, a golden statue, and they decide to return it after cleaning it. The group then argue over whether or not they should dispose of the body, Laurel believing that they should bury it. However, a coin toss determines that they bury it. When they go to collect the body, they wrap it up in a carpet and carry it outside, however they're stopped by a cop who questions Connor about his car. The cop almost discovers the body but is distracted by a rowdy group of drunken students. On their way to the woods they stop at a convenience store for supplies to dispose the body with. They continue their journey into the woods and they're almost caught by two drunken teenagers who are there looking for some privacy. Laurel's phone rings, Frank having called her. The others wonder what is going on and why he would call. Once they leave and they're in the clear, they take the body to a secure location and decide for one final time if they want to get rid of the body. Everyone is now in agreement and end up burning the body, disposing of all the DNA.