Lehmann was honoured with the Athena City Accolade for lifetime achievement, and elected a member of the UK Academy of Urbanism.

• 1998 — Fellowship recipient, Werner-von-Siemens-Fellow of the Stiftung Werner-von-Siemens-Ring, Berlin

• 2010 — Award for Teaching Excellence, University of Newcastle, NSW, Australia

• 2016 — Appointed to the UK Academy of Urbanism, London

• 2020 — Global Top 100 Leader in Education Award, for pedagogical innovation, GFEL, USA

• 2021 — Athena City Accolade Award, Royal Institute of Technology KTH, Stockholm — Life achievement award for outstanding lifetime contributions to the field of sustainable architecture and urban design in both practice and theory.

• 2023 — Fielden Medal of Educational Excellence, UNLV School of Architecture — for excellence in architectural education and impactful scholarship, Las Vegas, USA