In "Middle Men", Lynn revealed that she had an extremely miserable life in her first year of middle school during the 6th grade. Back then, she was sweet and sensitive, but after being bullied multiple times, she thought that if she acted tough like everyone else, she would stop getting picked on. Although it worked, it has just caused her to become more aggressive over the years. But she is still caring and didn't want her brother or Clyde to suffer like her.
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, hockey, 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 competition - her siblings consider this to be her most annoying habit. She is also shown to be very competitive, and strives to be "number one" in every game she plays, even when winning isn't involved.
After Lola, Lori, and Luna, she is the fourth most easily angered Loud sibling and is the most prone to physical confrontations.
Despite her tomboyish attitude, she shows 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.
Lynn is very superstitious and makes up absurd assumptions, because 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 the baseball season. This is shown again in "No Such Luck", where she is shown to perform good luck rituals, and unfairly believes Lincoln is bad luck when he comes to her game and she loses, ruining her winning streak.
Lynn is also very immature, as shown in "Cereal Offender" when she rides on carts in the grocery store and wrecks several aisles. Another example of her immaturity is shown in "A Tale of Two Tables", where she participated in the food fight with her siblings. Another part of this immaturity is her poor sportsmanship. When she loses, she starts throwing tantrums, and if she wins, she starts gloating at others, until someone makes her realize she's hurting their feelings.
Lynn isn't exactly above employing underhanded methods in order to win. In "Space Invader", she complements Lincoln's wrestling ambush upon entering his room, even if it is considered cheating. Another instance occurs in "Lynner Takes All", when she tricks Lincoln into giving the wrong answer during a trivia game.
Although in "Net Gains", she may have finally learned true sportsmanship when she was put in a bad basketball team called Turkey Jerkies and since she was so blinded by winning the championship, that she forgot the real reason why they play basketball: to have fun. She even accepted her and the teams' loss with pride at the end.
In "Sitting Bull", it is revealed that her aggressive attitude causing her to abuse the kids that she babysat, which causes their parents to fired her older sisters. After she was placed to babysit the Fox quintuplets, she began felt like babysitting rather than child abuse.
"Lynn Loud can turn anything into a sport. Putting away eggs? Jump shot! Mopping the kitchen? Slapshot! 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 high ponytail. She wears a red and white jersey with a red "1" on it, red-and-white track shorts, and black cleats with striped white 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 night attire also consists off a white and red sports shirt with a 5 on it and red shorts. 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 is pretty much the same as Girl Lynn. Here, he shares the same room with Lars and Lincoln. The only thing different about him is the hairstyle.
However, Boy Lynn is shown to be even more rough towards Lincoln than Girl 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.
Boy Lynn eventually turns out to be a product of Lincoln's imagination as the entire adventure was a dream, though Lincoln states Girl Lynn somewhat acts the same as Guy Lynn 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.