After signing with Disney Channel in 2009, she played Juliet van Heusen on Wizards of Waverly Place (2009–2012) and soon rose to fame for her lead role as Teddy Duncan on Good Luck Charlie (2010–2014).

From 2010 to 2012, Mendler served as ambassador to nonprofit First Book, which encourages reading, and Give with Target, to raise funds to reform schools in the United States.

[8] When she was eight years old, Mendler began taking part in local roles in both dramatic and musical theatre, and became the youngest performer in the San Francisco Fringe Festival.

[15][16] To the University Star, Mendler said USC was important: "I think seeing that college life and what that would've been like, it does make you wonder what sort of lifestyle that would be, but I'm really grateful for what I have, and I think it's cool that, because my career path is not as formulaic, I can kind of decide when I want to take time off to do certain things.

In 2008, it was announced that Mendler would play the role of Kristen Gregory in the film adaption of the popular teen novel series The Clique by Lisi Harrison.

[37] She had begun working on a film with actress and singer Lindsay Lohan titled Labor Pains, which kept being pushed back due to various conflicts and problems.

Mendler portrayed the role of Juliet Van Heusen,[40] a vampire who later forms a romance with David Henrie's character Justin Russo.

[42]In 2010, Mendler became the star of the Disney Channel series Good Luck Charlie, centering on a teenage girl who makes videos for her baby sister to watch as she gets older.

[44] In 2011, she starred as Olivia White, the lead role in the Disney Channel Original Movie Lemonade Mouth,[45][46] watched by 5.7 million viewers on its premiere night.

[70] She appeared in the Netflix comedy film Father of the Year along with David Spade, Joey Bragg, Matt Shively and Jackie Sandler, which was released July 20, 2018.

[71] In November 2019, Mendler appeared in the eight-part Netflix comedy television series, Merry Happy Whatever, along with Dennis Quaid, Ashley Tisdale, and her Undateable co-star Brent Morin.

[75] Mendler recorded the song "This Is My Paradise" for Beverly Hills Chihuahua 2, which was released as a promotional single on January 11, 2011,[77] with a music video directed by Alex Zamm.

The tour primarily reached only North America and she played at state fairs, music festivals and Jingle Ball's concerts series.

[118][119] Mendler discussed some of the producers and songwriters she was working with, including Mitch Allan, Dan Book, Alexei Misoul, Augie Ray, Beloryze, TMS, Ina Wroldsen, and Steve Mac.

[134] The venture-backed company, where she serves as CEO, is based in El Segundo, California, and intends to mass produce satellite ground stations.

[143] In 2011 it became part of Disney's Friends for Change, a pro-social "green" initiative of charity for environmental issues encouraging fans to take action.

[143] As campaign theme that year Mendler released a promotional single on June 11, "We Can Change the World", raising $250,000 for the Disney Worldwide Conservation Fund.

Her passion for helping children truly came through when she met with families and kids during her visits to the remote communities in the deserts of California and Guatemala's western highlands".

[162] In 2012, Mendler signed with Target to release an exclusive line of clothing inspired by her character Teddy Duncan of Good Luck Charlie.

[163] The D-Signed by Teddy Duncan fashion collection includes clothing, accessories, hats, scarves, and souvenirs for girls in range from 4 to 18 years old.

[165] While promoting her debut single "Ready or Not", Mendler signed with The Hunt, a mobile app which combines clothes and shows fashion tendencies.

[177] During an interview with Yahoo!, in 2012, Mendler also commented that her first female influence was the R&B girl group Salt-N-Pepa and sang an impromptu a cappella rendition of the song "Shoop".

[184] In 2014, she mentioned in an interview to CKQK-FM Canadian artists Nelly Furtado, Joni Mitchell and European bands Coldplay and Little Dragon as influences in composing her second album.

[179] To Pop Dirt Mendler said: "I consider myself to be that girl sitting at the curb waiting for the world, so I think it's a great message to send to just go for the things that you want to take charge of".

[201] In 2012, Mendler was chosen as role model of the year by Common Sense Media, a non-profit organization that honors innovative minds from the worlds of entertainment, public policy and technology and rewards mainly teachers, scientists and philanthropists.

[146] She was honored for her charity work in anti-bullying actions, improving the lives of families by providing a trustworthy role model and creating a positive impact in the world.

[203] Carolina Malis of the South China Morning Post believed the role "truly showcased her versatility, blending acting with singing and setting the stage for a career that would soon blossom beyond the boundaries of teen stardom.

[211] Tim Sendra of AllMusic defined Mendler's voice as "idiosyncratic" while reviewing Hello My Name Is... and called it "an impressive debut from a singer who shows real talent and has every chance to break out of the Disney mold and do something all her own down the road."

"[213] Her second extended play Nemesis was reviewed positively by Ailbhe Malone of The Irish Times, who believed Mendler was "back and trendy," and described it as "delicate and interesting but still vibey.

"[214] Andrea Domanick of Vice agreed, believing that with Nemesis, Mendler "heeds honesty over any kind of carefully crafted post-Disney identity.