Melissa Hastings is a fictional character in the Pretty Little Liars franchise. Created in 2006 by Sara Shepard for the book series, the character was later reworked by I. Marlene King, the developer of the television series, in which she is portrayed by Torrey DeVitto. An antiheroine, Melissa is sister to protagonist Spencer Hastings, and the daughter of Peter and Veronica Hastings. She is a fierce woman who does everything to succeed in her life goals. In print, she is a guest character, while on screen Melissa has a much bigger presence in the story.

Melissa has had recurring appearances in most of the Pretty Little Liars novels, starting with the 2006 homonymous book. She also appeared in the 2012 companion novel Pretty Little Secrets. She is the daughter of Peter and Veronica Hastings, sister of Spencer Hastings, and half-sister to the twins Alison and Courtney DiLaurentis, which are the result of an affair her father Peter had with the twins' mother Jessica. Melissa attended high school at Rosewood Day School and graduated from the University of Pennsylvania. According to Spencer's description of Melissa, she closely resembles Mrs. Hastings with her chin-length ash blonde hair and blue eyes; Spencer sarcastically described her sister as "a perfect little clone." Melissa has an uptight, simpering personality to match her lack of style.

Melissa and Spencer are rivals sisters who compete for their parents' recognition and Melissa appears to be the favored child who can do no wrong. She always seems to one-up Spencer in everything from academic achievements to extracurricular actives. As she is about five-six years older than Spencer, she's essentially accomplished everything Spencer has done in high school. Problems occur when she begins to feel attracted to Melissa's new boyfriend, Wren Kingston, when he is introduced to the family. "A" eventually reveals to Melissa that Spencer is dating. Wren dumps Spencer while he is back hooking up with Melissa, and Melissa eventually dumps him, removing him for her and her sister's life for good. Ian returns from California and starts working as a field hockey coach, in Spencer's team, which allows Melissa to pursue him again. "A" reveals to Melissa that Spencer stole her essay for the Golden Orchid competition, but the family keeps quiet to protect their reputation. Melissa and Spencer grow closer, and Spencer confesses that she kissed Ian, and that he and Alison were secretly dating. Spencer and Melissa's feud continues anyway after Melissa confronts Spencer about seeing Ian behind her back, which Spencer denies. Spencer and Mona eventually start suspecting that Melissa may have killed Alison. Spencer and Mona discover a note from "A" and suspect that Melissa killed Alison because she was jealous of her relationship with Ian. Mona, Spencer and their friends decide to turn Melissa in, but eventually Mona is revealed to be "A" and the girls stop suspecting Melissa.

When Courtney DiLaurentis, Alison's twin sister, returns Melissa immediately has a bad feeling about her. Jason told her everything about the sisters a while ago and none of the stories matched up - Courtney claims that her and Alison were best friends who shared everything whilst Jason says they despised each other and the reason Courtney is in a mental clinic is because she attempted to strangle Alison. Melissa investigates Courtney, but gets too close to the truth and is kidnapped by Courtney. She wakes up bound and gagged in a wardrobe next to Ian's dead body, Courtney didn't have time to kill her then, but she was going to kill her later. The Liars were trapped inside the house by Courtney and discovered that Courtney was in fact Alison, who murdered the real Courtney after a case of mistaken identity. The house is set on fire and the Liars stumble upon Melissa in the wardrobe and free her, they all then manage to escape.

Throughout the rest of the books, Melissa becomes engaged to Darren Wilden and her and Spencer become closer. When Spencer's parents practically abandon her, Melissa supports Spencer throughout her hard time and tries to be a good sister.

The Hollywood Reporter noted that Torrey DeVitto and Sasha Pieterse landed recurring roles in the pilot. The Alloy Entertainment website later confirmed that Pieterse would be playing Alison DiLaurentis and DeVitto would portray Melissa Hastings.

In the show, Melissa's role is much greater and more mysterious. She has been accused of being "A" multiple times, and has held grudges against the Liars, yet has seemingly displayed affectionate and overprotective behavior towards her sister.

Melissa is first mentioned in the Pilot by Hanna Marin and her half-sister Spencer Hastings when they meet at the mall. The character makes her first official appearance in the same episode, commending Spencer for her efforts in renovating their barn. Melissa subsequently informs her sister that she alongside her fiancé, Wren Kingston, will be moving into the shed. This announcement angers Spencer because their parents agreed for her to move in instead. Wren later questions his sister-in-law if she's doing okay but Spencer storms out. Kingston proceeds to divulge Melissa that her sister doesn't seem too happy with them moving to the barn, but she assures him she'll get over it. Afterwards, Melissa reappears in a flashback with her ex-boyfriend, Ian Thomas, hanging out at the Hastings residence. Former next-door neighbor Alison DiLaurentis was present in the moment as well. Ali discloses to Melissa that her sister has something to declare, which Spencer abruptly disregards. Melissa and Ian proceed to leave.