He was educated at Brownell-Talbot, Harvard, and the University of California at San Diego, where he took his degree in engineering.
Occasionally uses his middle initial A (for Anthony) to differentiate him from others in the entertainment field with the same name. In 1971 he joined the staff of The Theatre Royal, Bristol and became part of the sound department in 1972. He ran the department on his own until 1976, providing soundtracks for the three theaters in the Bristol Old Vic"s stable.
The Theatre Royal, The New Vic Studio and The Little Theatre.
During his time at the Bristol Old Vic, he co-designed and built what was to become one of the first sound mixing boards designed exclusively for theatre, marketed as the Libra Theatre Desk. This was awarded the Association of British Theatre Technicians Product of the Year for 1979.
In 1978, he was invited to join the Royal Shakespeare Company and in 1984 he was made the company"s first head of sound and an associate artist of the company. Whilst there, he conceived and co-designed the ASSIST computer-aided sound-routing system.
A development, DAISY, a digitally controlled analog mixing board with assignable controls, was conceived in 1984, but shelved through lack of development funding.
He left in 1989 to pursue a freelance career, joining with fellow sound designers John Owens and Fergus O"Hare to form Aura Sound Design in 1998. The company closed down in 2004 with the partners all pursuing separate careers. He has provided soundtracks for theatre productions in many countries and has designed exhibition systems for the Tussauds Group in London, Amsterdam, New York and at Warwick Castle.
As an author, he has contributed to "Effects Foreign Theatre", published by A&C Black/Routledge and is the author of "Theatre Sound" for the same company.
He writes regularly for Live Design magazine and contributed extensively to the British Broadcasting Corporation Radio 4 series on theatre sound "From Megaphone To Microphone." He also authored Theatre Sound. Leonard has been an innovator in many fields of theatre sound design, including promoting the use of stereo and surround material, specialist sound mixing boards, computer assisted routing systems and the use of computers and samplers for playback purposes.
He is an advocate of surround recording using the Ambisonic system and has collected a large sound effects library recorded in the four channel system known as B-Format. He is an Honorary Fellow of The Guildhall School of Music and Drama and of the Hong Kong Academy for Performing Arts and guest lecturer at a number of drama colleges in the United Kingdom and the United States.
Leonard married the cellist Andrea Hess in January 1985.
They live in North London.