[8][11][12] At 9 years old, Platt played Winthrop Paroo in The Music Man at the Hollywood Bowl alongside Kristin Chenoweth.

[19] In 2015, Platt reprised his role as Benji Applebaum in the sequel, Pitch Perfect 2, followed by appearances in the films Ricki and the Flash and Billy Lynn's Long Halftime Walk.

Platt became attached to Steven Levenson and Pasek and Paul's then Untitled P&P Project in 2014, participating in early read-throughs and workshops.

[23] In December 2016, Platt originated the title role in Dear Evan Hansen on Broadway at the Music Box Theatre.

[30] On January 28, 2018, he performed Leonard Bernstein's "Somewhere" live at the 60th Annual Grammy Awards accompanied by Justin Goldner and Adele Stein and arranged by Alex Lacamoire.

[34] Platt starred opposite Damian Lewis, Nina Dobrev, and Mena Massoud in the Rob Ford historical fiction thriller Run This Town.

[35] The casting of Platt caused minor controversy, over allegations that the filmmakers were appropriating the story of female reporter Robyn Doolittle.

[36] On March 1, 2018, Platt was confirmed to star in the indie drama Broken Diamonds opposite Lola Kirke, Yvette Nicole Brown, Alphonso McAuley, and Lynda Boyd.

[43] On August 29, 2019, it was announced that Platt would be starring in Richard Linklater's film adaptation of Merrily We Roll Along alongside Beanie Feldstein and Blake Jenner.

The project is set to be shot over the course of twenty years, with principal photography of the first sequence of the film having already been completed prior to the announcement.

[46] Platt starred as Payton Hobart on the Netflix comedy-drama series The Politician, which tells the story of a very driven teen convinced that he's destined to become President of the United States.

[52] On June 8, 2020, Platt released "Everything I Did to Get to You", a new single written by David Davis, which he picked as the winner of his episode of NBC's songwriting competition show Songland.

[55] The Reverie tour was announced on August 13, 2021, spanning 27 stops in North America beginning February 23, 2022, and concluding at the Hollywood Bowl on April 8, 2022.

[56] The tour was later postponed due to the COVID pandemic and rescheduled to begin on September 3, 2022, in Seattle, Washington before concluding in Hollywood, Florida on October 7, 2022, for a total of 20 stops.

[57] On June 25, 2021, Platt released a cover version of the song "Yoü and I" by Lady Gaga, as part of the tenth anniversary of the Born This Way album.

[58] On June 18, 2020, Platt confirmed that he was set to reprise his role as Evan Hansen in the film, which would be directed by Stephen Chbosky from a screenplay by Levenson.

Platt, however, dismissed the response, comparing his age to those of actors who played high school students in the 1978 film Grease.

On August 8, 2021, in an interview with Zach Sang on his YouTube talk show, Platt said "I think the reaction is largely from people who don't understand the context of the piece — the fact that I created the role and workshopped it for three years ...

"[63] On March 2, 2021, it was announced that Platt was in talks to star in the film adaptation of Grant Ginder's novel The People We Hate at the Wedding.

The film began production in September 2021 and was released worldwide on streaming platform Amazon Prime Video on November 18, 2022 .

[72] On the night of the show's first preview, members of the neo-Nazi group National Socialist Movement protested against the production outside the theater.

[77][78][79] The movie soundtrack featuring original songs written by Platt, Galvin, Gordon, and Lieberman was released on the same day by Interscope Records.

[80] On August 31, 2022, before kicking off the Reverie Tour, Platt confirmed that he was working on new solo music and was a third of the way through completing his next album.

[84] The residency ran for 18 performances between May 28, 2024, and June 15, 2024, and included special guests Kacey Musgraves, Kristin Chenoweth, Alex Newell, Kristen Bell, Meghan Trainor, Cynthia Erivo, Laura Dreyfuss, Micaela Diamond, Gaten Matarazzo and Brian d'Arcy James.

[129] Platt reprised the role in the 2021 film adaptation earning a nomination for the Golden Raspberry Award for Worst Actor of the year.