At 13 years old, Lynn is the fifth-oldest child of the Loud family, and the youngest of Lincoln's five older sisters. She is named after her father. Her most annoying habit is turning everything into a sport.
Lynn is athletic and competitive. She loves to play sports and enjoys roughhousing with her siblings.
She enjoys playing every existing sport, including football, soccer, basketball, and baseball. She is also skilled in various forms of martial arts such as kickboxing, Mexican wrestling (or lucha libre) and parkour. As seen in "Undie Pressure", Lynn tends to turn everything into a sport - her siblings consider this to be her most annoying habit. She is also shown to be very competitive and strives to be "number one" on every sports team she plays on.
After Lola and Lori, she is the third most easily angered Loud sibling, and is the most prone to physical confrontations.
Despite her tomboyish attitude, she has no shame in using puppy eyes to get what she wants, such as bunking in Lincoln's room in "Space Invader". In "Heavy Meddle", she gets as excited as her sisters after finding out about Lincoln's romantic situation.
She appears to be superstitious, as in "Sleuth or Consequences", where she tells Lincoln that she never "bombs the toilet" before a big game of roller derby, because it's bad luck. This is also prominent in "Intern for the Worse", where she doesn't allow her teammate, Margo, to use the bathroom, because of the same belief. In "Cover Girls", she tells Lincoln to cover for her while she is at the batting cage to hit baseballs to avoid spring cleaning, and she said if she didn't hit the first ball, she'll have bad luck all throughout her baseball season. This is shown again in "No Such Luck", where she is shown to perform good luck rituals, and believes Lincoln is bad luck when he comes to her game and she loses, ruining her winning streak.
Despite her age, she sometimes acts childish, as shown in "Cereal Offender", when she rides on carts in the grocery store. Another example of her immaturity is shown in "A Tale of Two Tables", where she participated in the food fight with her siblings.
"Lynn Loud can turn anything into a sport. Putting away eggs? Jump shot! Mopping the kitchen? Slap shot! Lynn is very competitive and superstitious when it comes to her favorite teams. Plus, she can never resist a dare!"
Lynn has thick brown hair pulled back into a short ponytail. She wears a red and white jersey with a red "1" on it, red-and-white shorts, and cleats with striped knee-high socks. She is slightly taller than Lincoln, and has freckles on her cheeks. Despite her age, her appearance makes it seem like she's a preteen, not a teenager. Like most of her siblings, she has purple-gray eyelids.
Her night-time attire consists of a white tank top, red shorts, and ankle high socks. In a few instances, she is shown wearing a nightshirt that looks like her regular jersey, with socks instead of her usual sleepwear. Her swimwear is a red-and-white surf shirt with matching swim trunks.
In "One of the Boys", a male version of Lynn appears in the alternate universe where Lincoln has brothers instead of sisters. Unlike the others, he has the same name as his female version, and has the same athletic nature as such. Here, he shares the same room with Lars and Lincoln.
However, he is shown to be abrasive, and even harsher towards Lincoln than Lynn, punching him for little, to no reason, and playing keep-away with the time watch Lincoln used to travel to the alternate universe. In another alternate universe where Lincoln is female, he is shown to be caring and protective, like the female Lynn.
Lynn eventually ceases to exist as the entire adventure was a dream, though Lincoln states Lynn somewhat acts the same as her boy version does.
In the minicomic Deuces Wild!, Lynn interprets the superheroine called Strong Suit, who is also one of Ace Savvy's sidekicks. She has super strength. In the comic, she is summoned by Savvy (played by Lincoln) alongside the rest of Savvy's deck (played by the rest of her sisters) to help him and One-Eyed Jack (played by Clyde) to defeat the gas monster. After they defeat it, they prepared to fight against a garbage monster.