At thirteen Pleeth won a two-year scholarship to study with Julius Klengel at the Conservatory in Leipzig.
The same year he also made his debut as soloist with the Leipzig Gewandhaus Orchestra with Haydn's Cello Concerto in D major.
In 1933 he played in many BBC broadcasts and made his debut at the Aeolian Hall in London with the Dvořák Concerto as a soloist of the City of Birmingham Symphony Orchestra conducted by Leslie Heward.
In 1940, Pleeth performed the Schumann Cello Concerto with the BBC Symphony Orchestra conducted by Sir Adrian Boult.
Among the other composers who wrote pieces for Pleeth were Benjamin Frankel, Gordon Jacob, Franz Reizenstein, Mátyás Seiber and Bernard Stevens.
In 1952 Pleeth formed the original Allegri String Quartet with violinists Eli Goren and James Barton and violist Patrick Ireland.
Not only is the concert itself an exciting experience but it is the satisfaction of working out a piece of music with three other human beings for whom you have affection.
Some of his hundreds of other students are Robert Cohen, Frans Helmerson, Felix Schmidt, Stephen Lansberry, Natasha Brofsky, Colin Carr, Anssi Karttunen, Andrew Shulman, Martin Rummel, Paul Watkins, Sophie Rolland and his own son Anthony Pleeth.
The Brindisi String Quartet, Trevor Pinnock and Anthony Pleeth performed Haydn, Mozart and Schubert.
On 12 January 2000 the William Pleeth Memorial Concert was held at the St John's Church in London.