Olivia Olson, born on May 21, 1992, in Los Angeles, California, is an American actress, singer-songwriter, and writer. She was adopted at birth by writer Martin Olson and raised in a creative household. From a young age, she showed a passion for singing and acting, which led her to pursue a career in the entertainment industry. 

She graduated from Agoura High School in 2010 and is of Afro-Jamaican descent through her biological father.

Her career began with her role as Joanna Anderson in the 2003 holiday film "Love Actually," where she performed the song "All I Want for Christmas Is You." Her singing talent was so impressive that the film's director, Richard Curtis, had to make it sound more believable by adding the sounds of inhalations to the track. 

This role brought her into the mainstream and led to guest spots on shows like "The Ellen Show" and "The Tracy Morgan Show." In 2017, she reprised her role as Joanna in the short film "Red Nose Day Actually."

From 2008 to 2015, she voiced the character Vanessa Doofenshmirtz in the Disney animated series "Phineas and Ferb." She also voiced Marceline the Vampire Queen in the popular animated series "Adventure Time" from 2010 to 2018. 

Her voice acting career includes roles in other animated series such as "The Powerpuff Girls," "Steven Universe," and "Milo Murphy's Law." In addition to her voice work, she has appeared in live-action roles and performed in live theater, including venues like the Comedy Central Stage and the HBO Theater.

Her personal life has been relatively private. She lives with her father, Martin Olson, mother Kay Olson, and brother Casey Olson. She is currently dating musician and producer Nick Goldston. Olson enjoys a lifestyle that reflects her creative passions, including songwriting and voiceover work. 

She has also posted original songs on her YouTube account, showcasing her musical talents.

Throughout her career, she has received recognition for her work in both acting and singing. She has been praised for her performances in "Love Actually" and her voice roles in "Phineas and Ferb" and "Adventure Time." 

Her ability to bring characters to life through her voice and her dedication to her craft have earned her a loyal fan base and critical acclaim.