She has appeared in films such as What Women Want (2000), Fast Food Nation (2006), The Help (2011), and Much Ado About Nothing (2012), and is a cast member on the Dungeons & Dragons web series Critical Role (2015–present).

(2004–2006), Gwen Tennyson in the Ben 10 franchise (2008–2014), Renet Tilley on Teenage Mutant Ninja Turtles (2012), Shiseru on Naruto: Shippuden (2015), and Tulip Olsen and Lake on Infinity Train (2019–2020), Pike in The Legend of Vox Machina (2022–present), as well as the video game characters Gortys in Tales from the Borderlands (2014) and Petra in Minecraft: Story Mode (2015–2016) and its sequel (2017).

[4] He started a new job nine days after Johnson was born and subsequently moved the family to Franklin, Michigan, where they lived for a few years before returning to California and settling in Los Angeles.

[9] Johnson's career began at age six, when she played the role of Chrissy Seaver on the sitcom Growing Pains from 1990 to 1992.

In the one season series Phenom (1993–94), she played the mischievous younger sister of a rising teenage tennis star.

[11] As a voice actress, Johnson's earlier roles included Sean in the English dub of The First Snow of Winter, Gretchen Grundler on Disney's Recess, Terra in the second and fifth seasons of Teen Titans, Jinmay on Super Robot Monkey Team Hyperforce Go!

[29] In November 2019, Amazon Prime Video announced that they had acquired the streaming rights to this animated series, now titled The Legend of Vox Machina;[30] Johnson reprised her role as Pike Trickfoot.

[37] In October 2021, Johnson's Exandria Unlimited character Fearne Calloway returned in Critical Role's third campaign.

[40] In 2015, they created and starred in Little Things, a web miniseries on YouTube about two friends living in Los Angeles and their habit of making awkward everyday situations even worse.

[41] The first campaign of Critical Role began two years prior to the start of the series as a one-off, simplified Dungeons & Dragons game for Liam O'Brien's birthday.

[43][44] After Felicia Day heard about the private home game from Johnson, she approached the group about playing it in a live-streamed format for Geek & Sundry.

[45][46] Johnson enjoys singing and can play the guitar, piano, violin, and cello; she occasionally posted covers of songs on her SoundCloud page until late 2012.

[47] Her performance as Ellie in The Last of Us Part II included acoustic guitar covers of "Future Days" by Pearl Jam, "Take On Me" by A-ha, "True Faith" by New Order, and "Through the Valley" by Shawn James.

[48] She also joined co-star Troy Baker (in character as Ellie and Joel) to perform a cover of Johnny Cash's rendition of "Wayfaring Stranger", which plays over the end credits of the game.

[51] In 2012, Johnson began dating writer and musician Brian W. Foster, who also went on to host the Critical Role after-show Talks Machina.