At seventeen years old, he directed and starred in You're a Good Man, Charlie Brown at a high school theatre festival at the Fulton Opera House, for which he won a community award.

[10] Groff graduated from Conestoga Valley High School in 2003 and intended to attend Carnegie Mellon University, but he deferred his admission for a year when he was cast as Rolf in a Non-Equity national tour of The Sound of Music.

[14][15] That same year, he made his Broadway debut as an understudy for the lead role (played by Christopher Hanke), swing, and dance captain for the musical In My Life by Joseph Brooks, opening on October 20 and closing on December 11, 2005, after 61 performances.

[17] His breakout performance occurred in 2006, when Groff originated the lead role of Melchior Gabor in the Broadway production of the rock musical Spring Awakening.

The musical tells the story of repressed adolescents in late nineteenth century Germany discovering their sexuality, adapted from Frank Wedekind's original 1891 play by Duncan Sheik and Steven Sater and directed by Michael Mayer.

[20] Charles Isherwood of The New York Times called the show a "brave new musical, haunting and electrifying by turns" and praised Groff's "ardency and thoughtfulness".

[24] From July 22 through August 31, 2008, Groff played the lead role of Claude in the Shakespeare in the Park production of Hair, a rock musical about hippie counterculture during the Vietnam War that was directed by Diane Paulus.

[25] Theater critic Ben Brantley of The New York Times wrote in his review of Hair that "Mr. Groff, who was memorably tormented by young lust in the musical Spring Awakening, is even more affecting here, his open face a shifting map of doubt and affirmation.

[28][29][30] From November 14 to December 21, 2008, Groff appeared as Billy Noone, a closeted gay soldier fighting in Iraq, in the off-Broadway production of Prayer for My Enemy, a play written by Craig Lucas.

[33] From April 10 to May 17, 2009, Groff appeared as Gray Korankyi and Walter Riemann in the off-Broadway production of another Craig Lucas play, The Singing Forest, alongside Olympia Dukakis at the Public Theater.

[34] The play, directed by Mark Wing-Davey, was described by critics as "convoluted" in plot but with strong performances, praising Groff for his "natural emotional transparency [that] helps add layers to Gray".

[36] Groff starred as Dionysus in the play The Bacchae opposite Anthony Mackie from August 11 to 30, 2009; it was directed by JoAnne Akalaitis and produced as a part of the Public Theater's Shakespeare in the Park.

[40][41] From August 21, 2010, to January 15, 2011, Groff made his West End debut in the London revival of Deathtrap, a play written by Ira Levin and directed by Matthew Warchus at the Noël Coward Theatre.

The play received positive critical reception; The Spectator called Groff's performance "magnetic" and "deeply charismatic" but found the "relationship between student and professor [to be] unconvincing".

[51] Charles McNulty of the Los Angeles Times praised Groff's performance for its "admirable clarity" and wrote that "he is every bit as effective in revealing the delicate nuances of [his character].

[56] In 2013, Groff voiced Kristoff, a rugged mountain man and love interest to Anna, and his reindeer Sven in Disney's animated feature Frozen, alongside Idina Menzel, Kristen Bell, and Josh Gad.

"[66] Groff portrayed Craig Donner in The Normal Heart directed by Ryan Murphy, the film adaptation of Larry Kramer's autobiographical play of the same name, which depicts the New York City AIDS crisis in the 1980s.

Groff returned to the London stage on May 19, 2015, to star as J. Pierrepont Finch in a one-night-only concert of the musical How to Succeed in Business Without Really Trying, at the Royal Festival Hall alongside Cynthia Erivo.

[68] One critic from BritishTheatre.com wrote that while the concert lacked "consistent careful handling", Groff was "truly terrific" and "exudes a warmth and comic intelligence which makes him impossible not to watch.

Off-Center staged concert series and was directed by James Lapine, with Groff performing alongside Aaron Lazar, Dan Fogler, and Ana Gasteyer.

"[71] On March 3, 2015, Groff joined the cast of the hit musical Hamilton by Lin-Manuel Miranda and directed by Thomas Kail, replacing Brian d'Arcy James in the role of King George III.

[73] Ben Brantley of The New York Times called Groff's performance "delicious" and wrote that "His is the voice of vintage Britpop, rendered in a leisurely, ironic, condescending vein to a distant population he regards as savages.

[75] In October 2017, Groff starred in the Netflix crime thriller series Mindhunter, created by Joe Penhall and executive produced by David Fincher and Charlize Theron.

[86] From September 17, 2019, to January 19, 2020, Groff starred in the off-Broadway revival of Little Shop of Horrors at the Westside Theatre as Seymour Krelborn, a florist who raises a plant with a thirst for human flesh, alongside Christian Borle and Tammy Blanchard.

[87] The revival, directed by Michael Mayer, received rave reviews; The Hollywood Reporter wrote that Groff was "never-better ... hilarious, endearing and in tremendous voice" and that he "disappears into a role he was born to play".

[90][91][92] In November 2019, Groff reprised his role as Kristoff in the sequel film Frozen II, singing a solo song for the movie titled "Lost in the Woods".

[99] In December 2020, it was announced Groff would be joining the cast of Invincible as Rick Sheridan, an Amazon Prime Video adult animated superhero series based on the comics of the same name created by Robert Kirkman, with the first episodes expected to be released on March 26, 2021.

[124] In December 2015, he was honored by Equality Pennsylvania with the Bayard Rustin Award, which "recognizes a Pennsylvanian who is continuing the work to ensure that the LGBT community will be visible, accepted, and celebrated in our society".

[137] In August 2020, Groff joined the Hamilton cast in organizing the virtual fundraiser event Ham4Change for organizations working to end systemic racism, raising over $1 million for the Equal Justice Initiative, African American Policy Forum, Black Emotional and Mental Health Collective, Black AIDS Institute, Color of Change, Dance4Hope, Know Your Rights Camp, Law Enforcement Accountability Project, Until Freedom, and When We All Vote.

[149] On December 13, 2020, Groff and fellow Hamilton cast-member Sasha Hutchings hosted a virtual holiday concert fundraiser to support the campaigns of Jon Ossoff and Raphael Warnock in the Georgia Senate runoff elections.