Beverly Marsh is one of the seven members of The Losers Club. She is sexually abused by her father, Alvin Marsh, and bullied by Gretta Keene and some of the other students at school because of rumors of her being promiscuous. She is best friends with Bill Denbrough, Richie Tozier, Eddie Kaspbrak, Stan Uris, Ben Hanscom, and Mike Hanlon. Beverly also has a crush on Bill.
In the book she’s described as a really pretty girl with auburn hair that reaches her shoulder blades, lovely gray-green eyes and milky skin with a spray of freckles. In the 1990 mini-series, she has chest-length brunette hair and in the 2017 film adaption, she has red hair.
Beverly is known to be very insecure, due to her uneasy life at home because of her father's abusive nature, and being picked on at school most of the time. Nonetheless, she is very good-hearted.
While Beverly is in the girls’ bathroom, Gretta Keene bursts in and bullies her. Another girl pulls the trash bag out of the trash can, and proceeds to dump its contents on Beverly’s head; Beverly immediately holds her backpack above her head for protection. As Ben is getting his bike, Beverly steps outside and talks with him, telling him that Henry Bowers and his cronies are by the west entrance. She jokes around with him before introducing herself and signing his yearbook.
While Bill, Eddie, and Stan are in Mr. Keene's pharmacy collecting supplies to help Ben recover from his injuries that Bowers caused, Beverly is also in the pharmacy, and comes into their aisle to avoid Gretta. They explain their situation to her, and she distracts Mr. Keene long enough for the three to sneak out with their supplies. As Eddie is attending to Ben's wound, Beverly turns up again, and Bill invites her to go to the quarry.
Returning home, her father, Alvin, confronts her, and gets hands-on with her. Disgusted, Beverly goes into the bathroom and cuts her hair. The next day, as Bill, Eddie, Ben, Stan, and Richie are at the edge of a cliff overlooking a lake, Beverly shows up and jumps off the cliff, much to the boys' disbelief. After the six go for a swim, Beverly sunbathes; Stan, Richie, Ben, Bill, and Eddie can't help but look at her, and turn away when she looks toward them, and joins them as they look at Ben's history of Derry. They then go to Ben's house, where he shows them more of the town's history, and Beverly exposes Ben's interest in the New Kids on the Block.
That evening, Beverly finds a postcard from Ben in her backpack, and goes into the bathroom to read it, feeling good that someone has a thing for her. She then hears voices coming from inside the sink. Going downstairs into the den where her father is sleeping to grab a tape measure, she puts it into the drain as far as it can go; pulling it back up, it comes out covered in blood. Without warning, tendrils grab Beverly's wrists, and then wrap themselves around her, pulling the shrieking girl closer to the drain. Suddenly, blood shoots out of the sink, right in Beverly's face and all over her and the bathroom. Whimpering, sobbing, and screaming, Beverly backs away from the sink over to the bathtub. Her father, obviously awakened by her shrieking, enters the bathroom, but doesn't see the blood all over the bathroom, and is surprised to see that Beverly cut her hair.
The next day, Beverly summons Bill and the others to her apartment and shows them her blood-covered bathroom; they help her clean it up. While doing so, Bill starts to grow close to Beverly as well, making Ben slightly jealous. The six of them then save Mike Hanlon from Henry Bowers and his minions, after which, he joins the group.
Around the fourth of July, they talk about how kids disappearing is all too common as of late. Ben explains that he pieced together some of the events from the past and discovered that these incidents only happen every twenty-seven years. The seven of them then discuss things that they're scared of, with Mike explaining that his grandpa always believed that the town of Derry is haunted, and that the bad things are the work of one thing, something evil. In the garage at Bill's house, Bill uses a projector to project an old map of Derry, provided by Ben, to chart the locations of the incidents from the past, and find that they're connected by the sewers, and they meet up at the Well House. They are then attacked by a gigantic Pennywise, who goes for Beverly; Ben manages to repel him by reopening the garage door.
Bill then heads for the Well House, leaving Ben, Beverly, Richie, Eddie, Stan, and Mike behind. They follow him to the house and try to talk him out of going inside. Bill says that no adult in Derry is going to do anything about Pennywise. Eddie and Richie end up going inside with Bill while Beverly and the others wait outside. However, they are separated. Fortunately, Bill and Richie manage to get to Eddie just before Pennywise has a chance to devour him. Beverly, followed by Ben, Mike, and Stan, enters the house and stabs Pennywise through the head; he recoils, and Bill follows him, and sees him disappear into the well in the basement.
Afterwards, Eddie's mom, believing Bill and the others were responsible for his broken arm, forbids them from having any contact with Eddie. Richie, Stan, and Ben, angry with Bill for almost getting them killed, defect from the group. Beverly tries to convince Mike to stay, but he, too, declines, stating that he's an outsider, and that's the way it has to be. Beverly and Bill spend the rest of the month at home, all alone.
When August comes around, Beverly is about to head out to spend time with her friends, only to find that the door is locked. Her father expresses his uneasiness about her spending her whole summer with Bill and his friends, then confronts her about the postcard Ben gave to her, which he found in her underwear drawer, roughly grabbing her hand in anger and asking if she's still his daughter, to which she replies "No!". A fight breaks out between them; Beverly cripples him by kicking him in the balls and then in the face, then goes to hide in the bathroom. Alvin bursts into the bathroom, and pulls open the shower curtain to find her in the bathtub; she immediately bashes him in the head with a toilet tank lid, presumably killing him. Beverly looks at his seemingly lifeless body, then turns to leave the bathroom, only to come face-to-face with Pennywise, who grabs her by the throat and takes her hostage.
Bill arrives soon after, discovers that Beverly has been taken, then goes to alert the others, who he is still estranged from, and they hurry back to the Well House. As the six boys descend into the well in the basement, Beverly regains consciousness within Pennywise's hideout, in the bowels of the sewers, and tries to escape, but is ambushed by Pennywise, who shows her his true form, entrancing her. Bill, while tailing a shade of his missing little brother, Georgie, finds her in the hideout, and tries to get her down from her levitating state before being distracted by "Georgie" again. The others, while chasing Bill, locate her; Ben, Mike, and Richie manage to pull Beverly to ground level; Ben desperately tries to awaken Beverly, to no avail, then kisses her, which does the trick.
Catching up with Bill as he converses with "Georgie", eventually realizing it's a hoax, they are confronted by Pennywise. They attempt to fight him, but are overpowered, and Bill is ensnared by him; he offers to spare them in exchange for Bill. They refuse, eager to fight to the end. After taking a considerable beating from them, Pennywise assumes the form of Beverly's father as she stabs him in the mouth. Spooked now that he sees the kids aren't afraid of him anymore, he backs away in terror and falls down a pit, going into early hibernation. As Bill finds what's left of Georgie's raincoat, and has solid proof that he's dead, Beverly and the others join Bill in mourning for his brother.
In September, as they sit by a creek, Beverly tells them that, while entranced, she had a vision of them as adults, fighting against Pennywise, and doubts she'll forget it. Bill then has them swear that if Pennywise ever returns, then they'll return to put an end to him by making a blood oath, which involves him cutting the palms of their hands and forming a circle. Afterwards, Stan, Eddie, Richie, Mike, and Ben leave one by one. Beverly tells Bill that she's more or less ready to go to Portland the next morning, and that her aunt is allowing her to stay as long as she pleases, and also explaining that she never felt like a loser while spending time with Bill and his friends. She then gets up to leave; a few seconds later, Bill gets up, runs after Beverly and kisses her. Beverly passionately returns the kiss, bids Bill a fond farewell, and walks off.
After the events of the summer of 1989, Beverly has grown up and become a fashion designer in Chicago, while having gone through numerous abusive relationships over the years, including her marriage to Tom Rogan, who considers her a sex object. When she gets word that Pennywise is causing trouble around Derry again, she, Ben, Bill, and Eddie return to their childhood home town to eliminate the creep as promised.
- The 2017 remake implies Beverly had recently experienced her first period. Given she was looking at tampons at the drug store.
- In the novel, she is described by Stephen King having red or auburn hair, but in the 1990 miniseries, she has brown hair while in the 2017 film, she is a redhead.
- She is both the love interest of Bill and Ben who both kiss her in the 2017 film.
- She uses a slingshot to defeat It in the novel and in the miniseries but in the 2017 film, she beats It up and impales him with a rebar.