Marnie is the only child between her mother Evie, and her father; whom she mentions not having a good relationship with. Her parents divorced sometime during her childhood. She met Hannah while they were roommates at Oberlin College, where they also knew Jessa. Elijah introduced her to her now ex-boyfriend Charlie during their sophomore year at the Galactic Safe Sex Ball back in 2007. She and Hannah moved to New York together after they graduated. At the start of the series, she works at a small gallery.
In the premiere, Marnie is struggling with the fate of her relationship with Charlie. She describes his touch as that of a "weird uncle." At Jessa's welcome home dinner, Marnie becomes angry when Hannah and Jessa both arrive late. To make matters worse, Charlie invited his bandmate, Ray, and a random girl to the dinner. With her patience wearing thin, she attempts to confront Jessa, but is sympathetic when Jessa announces that she is pregnant.
In Vagina Panic, Marnie schedules both Jessa's abortion and Hannah's STD test. At the clinic, Marnie begins to worry that she is unable to get pregnant herself, and claims she was born to be a mother. After Hannah comforts her, Hannah goes to have her test. When Shoshanna then reveals that she is a virgin, Marnie assures her that she is completely normal.
In All Adventurous Women Do, Marnie get's a call from Hannah about Hannah's HPV diagnosis, and starts crying. She later attends an art gala, where she meets Booth Jonathan, a prestigious and cocky artist. The two go outside together, where he predicts the two will eventually have sex. Marnie re-enters the gala, locks herself in the bathroom, and touches herself. She comes home to find Hannah dancing, and the news that Elijah is gay. The girls laugh and dance together.
In Hannah's Diary, Marnie's true feelings about her relationship with Charlie are revealed after he and Ray find Hannah's diary. When Charlie starts singing during his performance with Ray using Hannah's entries, Marnie calls Hannah a bitch and pours her drink on her.
In Hard Being Easy, Charlie breaks up with Marnie over what Hannanh wrote. She insists to Hannah that she will get him back , and sees Ray at his job since she doesn't know Charlie's address. Marnie then goes to Charlie's apartment for the first time. It's shown via flashblack how Charlie and Marnie met after she ingested pot brownies at a party and he comforted her. Charlie takes Marnie back saying they have to work on their relationship, but she breaks up with after they have sex.
When Hannah goes to visit her parent's for the weekendin The Return, Marnie tells her that she needs to ask them for money.
In Welcome to Bushwick a.k.a the Crackcident, Marnie sees Charlie performing at the rave, and decides to go talk to him in hopes of being friends. But she's interrupted by his new girlfriend, Audrey. She later runs into Elijah, and complains to him about Hannah, but Elijah points out that she hooked up with him when he and Hannah were still dating. She later calls Hannah to find her after she get's a cab, and ends up taking both her and Adam home.
With Marnie's emotions out of control over Charlie, and Adam's prescence in the apartment, Jessa tries to make her feel better in Weirdos Need Girlfriends Too by taking her out on the town. They meet Thomas-John, who repulses Jessa. The two decide to go back to his apartment, where Marnie and Jessa kiss, but leave after accidentally spilling wine on the Thomas's floor.
In the penultimate episode, Marnie is increasingly more irritated with Hannah as she's fallen behind on her half of the rent, and the two have a falling out.
Marnie is seen going shopping with her boss in It's About Time and she just came back from having a surprise lunch paid for by her boss. Marnie compliments her boss for it, but her boss regrettably tells her that was a consolation for laying her off. Marnie angrily lashes out and storms off.
She later attends Elijah and Hannah's house warming party, where she hooks up with Elijah. The two decided to keep it from Hannah. She then goes to Charlie's apartment and asks just to sleep over.
In I Get Ideas, Marnie attempts to get another job at an art gallery, but is told she doesn't belong in the art world. She then gets a job as a hostess at a club.
In Bad Friend, Marnie runs into Booth Jonathan, who takes her from her job to his apartment. After displaying his art to her, the two have sex. Soon after, Hannah arrives and calls Marnie out on having sex with Elijah, and has her admit that's she's not the "good friend" she always believes herself to be.
In It's a Shame About Ray, Marnie goes to Hannah's celebration dinner. To her shock, Charlie and Audrey are there as well. Audrey antagonizes Marnie for still having feelings for Charlie, and she leaves. Charlie follows her out onto the rooftop, where he tries to make a move. She responds by announcing her supposed relationship with Booth. Charlie angrily leaves Marnie alone.
In Boys, Marnie hosts an event for Booth after his assistant Soojin quits. She mistakenly has begun thinking her and Booth are dating, which he corrects. After Booth has an emotional breakdown, Marnie decides to cut ties with him and leaves. She then calls Hannah, and the two have a conversation in which they pretend they are better without the other.
In It's Back, Marnie learns from Ray and Shoshanna, who she was soothing after Jessa abruptly ran away, that Charlie has created a very successful app inspired by their break-up. After viewing his office and financial situation, Marnie is distraught. Ray then convinces her to follow her own true passion, which she reveals is singing.
In the penultimate episode, Marnie performs a song for Charlie at a celebration party for his app. He talks to her in private and tells her to get her shit together. The two then have sex on his desk.
In the season finale, Marnie and Charlie have begun engaging in casual sex, much to her disbelief. After a heated brunch together, the two ultimately confess their love for one another. She later visits Hannah's apartment after receiving a distress call from her, but leaves when Hannah hides under the bed. She's last walking going out with Charlie.
At the start of the third season, it is revealed that Marnie and Charlie are no longer together and that she is living with her mother. She also has begun working for Ray at Grumpy's. While Hannah, Adam, and Shoshanna venture to get Jessa from rehab, Marnie moves into her own apartment.
In She Said OK, Marnie discovers that Charlie has yet to remove an embarrassing Youtube video of her, and fights with the telephone assistant about removing it. That night, she throws Hannah's 25th Birthday party, where she forces Hannah to recreate a duet they did together in college.
In Dead Inside, Marnie catches Ray and Hermie watching the Youtube video and quits her job at Grumpy's.
In the Only Child, Marnie looks to Ray to tell her everything that is wrong with her. Surprisingly, this ends in the two having sex. Her and Ray continue to see each other as friends, because they have nobody else to
In Beach House, Marnie invites the girls to her mother's friend's beach house where they will stay the weekend. Marnie intends for the weekend to be healing for the girls' friendships, but it ends in total disaster after Shoshanna has a meltdown and the girls argue.
In Incidentals, Marnie goes to Ray's apartment only for him to end whatever they have going on. He claims he wants to end their arrangement as he desries a real relationship. Marnie leaves to the hotel room Hannah is staying for an article, where she meets Desi, a fellow actor who is in the same play as Adam, who expresses interest in her and her singing abilities.
In I Saw You, Marnie has begun working at Soojin's art gallery. That night, Marnie and Desi perform a song and the audience applauds. However, Marnie finds out that Desi has a girlfriend,Clementine, and sees them together with her own eyes. She goes to Ray's apartment, and Hannah catches the two having sex.
In the season finale, Marnie admits to Shoshanna that she's slept with Ray, which she reacts to very negatively. At the opening night of Major Barbara, Marnie gives Desi a guitar pick, and he passionately kisses her. At first she is pleased, until Clementine confronts her and says that their music plans are not happening. In the end, Marnie stands in the street spying on Clementine and Desi arguing.
Season Four Edit
At the start of the fourth season, Marnie and Desi are officially a folksong duo. They are also in a relationship, even though Desi still hasn't broken up with his girlfriend.
In Triggering, Marnie is only briefly seen in a video chat with Hannah.
In Female Author, Marnie and Desi attempt to land a record deal, but are told they have to meet the head of the studio first. Afterwards, the two fight about their lack of an actual relationship.
In Cubbies, Marnie shows Jessa and Shoshanna a song of her and Desi's, which neither of them particularly likes. After they mock her, she claims that the only one capable of a real opinion is Hannah, who she calls a "creative." Later, her and Desi are practicing together awkwardly. Marnie claims she's moved on. However, later that night, Desi shows up at Marnie's apartment and announces he's left Clementine. She consoles him, but learns he only dumped her because she was going to dump him. Though she seems hesitant, he performs oral sex on her.
Marnie goes to see Hannah in Sit-In, and is able to convince her to let Adam go and leave her apartment.
Desi and Marnie are now living together in Close-Up, but have an argument over how they approach their music.
Following an argument over Desi spending their record deal money in Tad & Loreen & Avi & Shanaz. Desi proposes to Marnie, and she happily accepts.During Ray's campaign party in Daddy Issues, Marnie tells Desi that she wants to wait to tell people about their engagement, then announces it to the whole room.She and Desi meet with their manager at Ray's to discuss their music, and and upcoming showcase in Home Birth. She later tries to call Desi as goes he missed their soundcheck, but is encouraged by Ray to do the showcase by herself. She goes on stage, and does really well.