Wendy in Casper Meets Wendy
While most consider another role on this list as Hilary Duff's debut, her first lead role actually came in this 1998 direct-to-video sequel to 1995's Casper. She played the classic Harvey Comics character (Casper's BFF), Wendy the Good Little Witch. Duff was only 10 when the film was released.
Lizzie in Lizzie McGuire
It wasn't until this Disney Channel series, which debuted two decades ago in January 2001, that Duff became a household name. She starred as the beloved titular teenage character while also voicing the animated version that expressed Lizzie's inner thoughts and emotions. The series aired 65 episodes through February 14, 2004 and even got a feature film in 2003 that followed Lizzie on a school trip to Rome. Duff was set to return to the character for a highly-anticipated sequel series, but it was ultimately scraped.
Kelly in Cadet Kelly
A year after becoming a Disney Channel fixture, Duff starred opposite Even Stevens star Christy Carlson Romano in her first DCOM, playing Kelly Collins, a free-spirited and fashion-forward eighth grader forced to enroll at her hew new stepfather's military academy.
Natalie in Agent Cody Banks
Duff joined Malcolm in the Middle star Frankie Muniz in this 2003 spy comedy about a 15-year-old who goes undercover for the CIA. She played the daughter of a scientist employed by an evil organization that the intelligence agency wanted intel on. The film marked her first major motion picture, hitting theaters two months before The Lizzie McGuire Movie. A sequel was released a year later, however she did not return.
Lorraine in Cheaper by the Dozen
For her third theatrical release of 2003, Duff starred as Lorraine Baker, one of 12 children raised by Steve Martin and Bonnie Hunt in this family comedy, a remake of a 1950 film of the same name. She returned as Lorraine two years later in the sequel Cheaper by the Dozen 2.
Sam in A Cinderella Story
In 2004, Duff starred in this modern take on Cinderella, playing Sam Montgomery, with Chad Michael Murray as her "prince" a.k.a her anonymous online pen pal. Plus, Jennifer Coolidge was her evil stepmother Fiona. The film was a hit and spawned four sequels—three direct-to-video and a fourth for Freeform—with Selena Gomez, Lucy Hale, Sofia Carson and Laura Marano following in her footsteps.
Terri in Raise Your Voice
That same year, she starred in this musical drama as Terri Fletcher, a teenager grieving the death of her brother (played by Jason Ritter!) who travels to Los Angeles to spend the summer in a music program against her father's wishes. Naturally, he finds out and things get very dramatic.
Tanzie in Material Girls
In 2006, Duff starred opposite her older sister Haylie Duff in this film loosely based on Jane Austen's Sense and Sensibility. The two rich and spoiled Hollywood socialiate sisters, heiresses to their family's cosmetics fortune, are given the ultimate wake-up call when a scandal involving the company's night cream strips them of their wealth. It's not the most beloved film in her oeuvre, but a campy delight nonetheless.
Yonica in War, Inc.
Two years later, she appeared in this political satire co-written and produced by star John Cusack as a risque Central Asian pop star (and secret daughter to Ben Kingsley's hitman Walken) named Yonica Babyyeah. Again, not exactly the most beloved film.
Olivia in Gossip Girl
In 2009, Duff returned to TV with a six-episode stint on the CW hit as Olivia Burke, a movie star who inexplicably strikes up a relationship with Penn Badgley's Dan after enrolling at NYU and becoming roommates with Jessica Szohr's Vanessa. The trio memorably had a threesome before Olivia, realizing Dan had feeling for Vanessa, ended things.
Kelsey in Younger
It wasn't until 2015, however, that she returned to TV in a major way, starring as literary editor (and eventual publisher of her own imprint) Kelsey Peters on the hit TV Land rom-com, heading into its seventh season later this year.