Emma Johnson was born in the London borough of Barnet on May 20, 1966. She began lessons on the clarinet at nine and from age 15 played in the National Youth Orchestra of Great Britain. Johnson won the prestigious BBC Young Musician of the Year Competition in 1984, and the following year debuted in the recording studio and at Barbican Hall, both in performances of the Mozart Clarinet Concerto. Johnson managed to continue her concert career on a limited basis as a student at Pembroke College, Cambridge, where she initially studied English. While there she took clarinet lessons from Jack Brymer and Sidney Fell. In 1987 John Dankworth wrote Suite for Emma for her, one of many major composers have written for her.
In 1991 Johnson won the Young Concert Artists Auditions in New York City and later gave her recital debut at Carnegie Hall. Throughout the 1990s Johnson made a string of popular recordings for ASV, which included two encore discs, in 1992 and 1994, respectively, and the 1995 Sir Malcolm Arnold: The Complete Works for Clarinet.
In 1996 Johnson was awarded an MBE from the British government. She has remained busy in the new century on all fronts, appearing not only in regular concerts but at festivals like the Mostly Mozart at the Barbican, where in 2006 she performed the Mozart concerto. Among her more acclaimed recordings is the 2009 Naxos CD of Dankworth's Suite for Emma and sonatas by Bernstein and Copland. Johnson has continued to earn acclaim for performances of traditional repertory; her 2012 recording of sonatas by Brahms, recorded like several other Johnson releases with pianist John Lenehan, was hailed by the Observer as "a landmark disc." She has also branched out into jazz and other vernacular genres, artfully mixed together on her 2016 release Clarinet Goes to Town. Johnson has performed and conducted workshops for children, sometimes using a musical dramatization of the Pied Piper story. The Times of London has called Johnson simply "Britain's favourite clarinettist."