Not much is known of Bronwyn and her brother Victor, besides that, they used to live in Swansea, a city in Wales. Before the home, they lived with an abusive step-father whom Bronwyn snapped the neck of when she was 10.
Bronwyn is first seen in the circus the peculiar children perform in, lifting a giant boulder the size of a refrigerator overhead. Emma claims she isn't so bright but is very loyal and it makes the two of them the best of friends. Bronwyn joins Jacob, Emma, and Enoch into modern day to awaken a murder victim of the Wights where they discoverDr. Golan is one of them. While they fight the hollow he releases on them, Dr. Golan invades their home and takes Miss Peregrine. She sheilds the chlidren with old shipwreck parts as they attempt to save Miss Peregrine who is being held captive in the Carinholm lighthouse.
As the sequel opens, the children are rowing their boats away from Cairnholm island as their search for Miss Wren's loop begins. The children take turns rowing in shifts since everyone is tired from the long trip. Bronwyn shares the luggage and is able to row tirelessly for hours she rows 4 to 6 people. She takes a leadership role in the journey by defending the others with her strength or comforting the younger children. She carries Caul, disguised as Miss Peregrine, for most of the story. When questioned by a train conductor, Bronwyn even pretends that the bird is a wind up toy. After she witnesses Caul kill one of Miss Wren's pigeons, she believes it is Miss Peregrine's doing and refuses to carry her anymore. Along with the other children, except for Jacob, Emma, and Fiona, she is taken into modern day and transported to Devil's Acre by the Wights.
Bronwyn is imprisioned for most of the story and is discovered when she incapacitates a guard that Jacob and Emma are fighting through her prison bars. After being freed, she plays a large part in chasing out the Wights and releasing other peculiar children. Once Caul is defeated, Bronwyn joins the efforts to help those who had their loops raided and restore Devil's Acre. Due to being present in the collapse of Abaton, Bronwyn resets her clock and beings to age at a regular pace. When Jacob is about to be taken to a mental instituion back in America by his parents, who don't believe the events of the past three books, she arrives with the others and stops their car with her strength.
Bronwyn is said to be a "mannish-looking" girl who hates dresses and almost always has bare feet.
In the film, she is portrayed by Pixie Davies.
Despite not being the brightest, Bronwyn cares deeply for all of her friends. She is very loyal and shows hesitation in betraying Miss Peregrine when the children want to sneak out to find the wight. She ends up going to protect her friends though. Many times throughout the novel she shows her courage and love for her friends by attacking the wight and hollowgast on multiple occasions, usually with a sudden surge of energy. She has shown at least basic medical knowledge by making a tourniquet for Millard.
Bronwyn also has a very strong maternal instinct for the other children, particularly Olive and Claire who are the youngest. She is said to be the one to read the children stories at night and tuck them into bed rather than Miss Peregrine. In Hollow City, she willingly gives up her bulletproof sweater (To the disapproval of Enoch ) to Esme, though her sister Sam had been very hostile to them. When the peculiars considered if they should fight or hide when they got Miss Peregrine back, Bronwyn declares (graphic novel at least) that if some of the peculiars stayed to fight, then she would protect the ones that didn't.
While she rarely ever swears, she does swear occasionally in certain situations such as when the peculiars were trying to escape Caul, reached a door, and Bronwyn found that it was locked from the outside.
Bronwyn is a strong-arm, which means she can lift heavy objects normally incapable of a human. It is unstated how much she can actually lift, but she has easily lifted a large boulder the size of a refrigerator over her head and carried it under her arm effortlessly. She also pulled a cargo hold's door off a sunken ship and carried it as a shield with Millard on her back. Bronwyn is also capable of holding light objects with ease without breaking them. It is stated that she is "as strong as 10 men".
Golan revealed that Bronwyn was unaware of how strong she was until she snapped her step-father's neck, which she seemingly had the motive to do. She broke his neck as he was horrible to her and Victor.
Victor is Bronwyn's brother. Though he was killed by a hollowgast, Enoch has used his peculiarity to bring him back to life for brief amounts of time. While Jacob was introduced to Victor, Bronwyn begged Enoch to bring him back for a short period of time.
Emma and Bronwyn are good friends; Emma is shown to have a neutral, but a mostly positive relationship with Bronwyn. Emma is definitely the closest to the strong girl.