In the first film, Fiona appears as a princess plagued by a curse that transforms her into an ogress each and every sunset. Locked in a dragon-guarded castle for several years until she is "rescued" by irreverent ogre named Shrek, whom she mistakes for a knight, Fiona is at first eager to have her spell broken via true love's kiss by Lord Farquaad so that they remain human, but later she comes to love Shrek.
- Main article: Shrek
In the first film of the series, Fiona first appears as an option for a princess bride selected by Lord Farquaad, who desires to become king in order to access dominant authority, in order to accomplish this dream. Ignoring warnings of a secret possessed by Fiona, Farquaad proceeds with his plan and decides to search for the women so he may marry her and become a king, though she is soon encountered by Donkey and Shrek, and at first the group holds hateful feelings toward one another. However, late one night, Donkey learns that because of a magical spell that had been cast on her years before, Fiona transforms into an ogress every night, but by morning reverts to her regular human form. Eventually, Shrek and Fiona start to warm up each other and perhaps even begin to fall in love, but this is interrupted when Shrek and Fiona get into a misunderstanding followed by Shrek bringing Lord Farquaad to get Fiona, who then proceed to a marriage. Shrek and Donkey interrupt Fiona's wedding ceremony and try to cancel any possibilities of her wedding Lord Farquaad, and her ogre transformation spell is triggered and manages to appall Farquaad into losing desires of marrying her. At the end of the movie, Shrek marries Fiona and Farquaad is swallowed by Donkey's new girlfriend, Dragon.
- Main article: Shrek 2
In Shrek 2, Fiona convinces Shrek to meet her parents in the kingdom of Far Far Away (resembling the shallowness of Hollywood). They go, and her Fairy Godmother, who had her locked away in the tower to begin with, still believes she is under the original curse. When the Fairy Godmother finds out that she is in fact married to an ogre, Fairy Godmother plots to kill Fiona's husband so her son, Prince Charming, can marry her. It turns out that there was a semi-complex plan where Prince Charming, not Shrek, was supposed to rescue Fiona and marry her. It was the King's way of repaying the Fairy Godmother for a favour she had done him while courting Fiona's mother. Fiona is briefly returned to human form from the first film after Shrek drinks a "Happily Ever After" potion, which changes both the drinker and their true love into more beautiful forms. To make the change permanent however, she must kiss her true love by midnight. Fairy Godmother tries to get King Harold to give his daughter a love potion so that she'd fall in love with Charming and kiss him to make the potion's effect permanent. Both plans ultimately fail however. Harold, after seeing how much Fiona despises Charming, does not give her the love potion. When Shrek tries to kiss Fiona, she tells him that she wants to live happily ever after with the ogre she married. She and Shrek then turn back into ogres, and Donkey (who had turned into a white stallion) turns back into a donkey.
Shrek the Third
- Main article: Shrek the Third
In Shrek the Third, Princess Fiona becomes the queen of Far Far Away while her father is ill. When the latter passes away, Shrek sets out to find her cousin Arthur Pendragon (or Artie). She tells him that she is pregnant (something that she has been hinting since the start of the film). While she is having a baby shower, Prince Charming stages an invasion so that he can proclaim himself king of Far Far Away. Fiona organizes the resistance with her friends Cinderella, Snow White, Sleeping Beauty, Rapunzel and Doris the Ugly Stepsister, but Rapunzel betrays them to marry Prince Charming. Thanks to her mother's fighting abilities, they escape prison, and the other princesses 'cut loose' and become more independent. Artie ends up making a speech to convince the villains to go straight. In the end, she gives birth to the ogre triplets with Shrek.
Shrek Forever After
- Main article: Shrek Forever After
During the babies' birthday party, Fiona sees Shrek steadily more irritated and eventually losing his temper by smashing one of the birthday cakes. Outside Fiona confronts him about his outburst. Shrek responds that he is sick of not having his privacy respected and that he wishes everything as "back to the way they used to be...when the world made sense". When Fiona asks him if he means before he rescued her, Shrek cruelly confirms her fear. Fiona is shocked and upset by Shrek's actions, she tells him that he had everything he could have ever wanted: "three beautiful children", "a wife who loves [him]" and "friends that [adore] him". She goes back inside to the party, disappointed in him.
When Shrek makes his deal with Rumpelstiltskin, for a single day he is brought to a universe where he was never born. Here, Rumpel has seized power by tricking Fiona's parents out of ruling the kingdom of Fat Far Away. Fiona remains under the witch's curse from the first movie and is subsequently become the leader of a group of Ogre resistance fighters. Shrek initially believes that the relationship between him and Fiona is existent but when she doesn't even recognise him, he finally accepts completely that the reality, he is in, is not his own and Stiltskin has truly altered reality to be as if he never existed until now. Fiona is still shown to still be kind hearted and caring but bitterly cynical and disillusioned about the power of true love, because she was never rescued from her tower. She begins to fall in love in him again when he starts training with her, but still does not kiss him (having only started to find him likable). But Fiona's attitude toward Shrek changes and she and the other ogres head off to take down Rumpelstiltskin once and for all. During the day, Shrek realises that a loophole will negate the deal if he can receive a True Love's kiss Fiona. After a failed attempt, the realize that he had succeeded when Fiona's curse has been broken. The timeline returns to normal, and Shrek returns to the children's birthday party and warmly greets Fiona. This is the only movie where Fiona has her hair down. She also reveals that she always wanted to have a daughter named Felicia. We also learn that Shrek and Fiona's sons are Fergus and Farkle.
- Fiona is the second DreamWorks character related to the protagonist to change a decision concerning the protagonist. Rameses II (the first to do so) initially allowed Moses and the Hebrews to leave Egypt, but pursued them to the Red Sea trying to kill them; Fiona decided to tell Shrek about her curse before leaving with Farquaad, but didn't do so).