Jonathan Sayer is a British actor and playwright. He co-founded Mischief Theatre, responsible for The Play That Goes Wrong, Peter Pan Goes Wrong, The Comedy About a Bank Robbery, Groan Ups, Magic Goes Wrong and The Goes Wrong Show. In 2008, Sayer, Henry Lewis, and Henry Shields co-founded Mischief Theatre while they were studying a drama foundation course at the London Academy of Music and Dramatic Art.

In 2012, Sayer co-wrote with Lewis and Shields The Play That Goes Wrong, which premiered later that year at The Old Red Lion, Islington. Sayer played Dennis Tyde in both the original London cast and the original Broadway cast. In 2013, another Lewis, Sayer and Shields production, Peter Pan Goes Wrong, premiered at The Pleasance Theatre. with Sayer amongst its original cast, playing Dennis.

In 2016, Lewis', Sayer's and Shields' play The Comedy About a Bank Robbery opened at the Criterion Theatre; Sayer was amongst its original cast, and played Warren Slax. In August 2019, Magic Goes Wrong, a play written by Lewis, Sayer, Shields, Penn and Teller, premiered at the Quays Theatre; Sayer played Mikey, and subsequently took him on tour. In September 2019, the next Lewis, Sayer and Shields play, Groan Ups, premiered at Vaudeville Theatre, as part of a projected year-long residency at the theatre (later curtailed due to COVID-19 restrictions) with Sayer playing Simon.

In 2016, a production of Peter Pan Goes Wrong was aired by BBC1, with Sayer playing Dennis. The following year, they aired A Christmas Carol Goes Wrong, with Sayer playing Dennis. BBC1 aired twelve episodes of The Goes Wrong Show between December 2019 and November 2021.