2013–2018: Adventure Time, Steven Universe, and Phineas and Ferb
In 2010, Olson got the role of Marceline the Vampire Queen on the animated Cartoon Network series Adventure Time. Olson said she was impressed by her character's fashion design and the costuming for Marceline, saying she occasionally admired the unique designs for the character in episodes. During the audition for the role, Olson first read for Princess Bubblegum, but later read for Marceline. Reportedly when getting into character for the role she often dressed similar to Marceline when she recorded her lines In the show, her father played Hunson Abadeer, the father of Marceline. In the series, Olson also sings Marceline's songs, which were written by storyboard artists, or other people affiliated with production. As such, The Guardian praised Marceline as a character, noting in particular that "she's ... responsible for some of the show's best songs."
The series was a commercial and popular success and her character attracted positive critical attention from critics, and fans alike, along with the production crew of Adventure Time. This popularity was even recognized by the company that owns Adventure Time with the official press release for the Adventure Time: Marceline and the Scream Queens companion comic book referring to Marceline as a "fan-favorite". Olson later said she was "honored" to be voicing a character in a show pushing the limits, including on "what a female character in a TV series brings to the table."
In the Adventure Time mini-series "Stakes", Olson performs the popular song "Everything Stays", which was revealed by Olson and Rebecca Sugar at the 2015 San Diego Comic-Con. In 2015 Olivia and her father, Martin Olson, co-authored a book adapted from the series Adventure Time, Adventure Time: The Enchiridion & Marcy's Super Secret Scrapbook. Olivia wrote her section in first person as her character Marceline. The book was illustrated by artists including Mahendra Singh, Tony Millionaire, Renee French, Celeste Moreno and Sean Tejaratchi.
Olson also performed the song "Haven't You Noticed (I'm a Star)", which was featured on the September 17, 2015, episode of Steven Universe entitled "Sadie's Song".
It was later featured in the Steven Universe mini-episode "Gem Karaoke", released on October 3, 2016. She appears at Comic-Cons and pop conventions around the world as do other Adventure Time cast members.
From 2016 to 2019, Olivia voiced the fourth Powerpuff Girl Bliss on Cartoon Network's reboot of The Powerpuff Girls, The character's initial announcement was met with negative reactions from some fans, but when rumors began to spread that the character would be black, fans began to express a more optimistic tone. Reviewers later called the character a great step forward in terms of racial diversity and a good addition. Reactions to the character were mainly positive, while others argued she was a stereotype and that the inclusion of the character seemed like tokenism.
