Wallen’s first major work, Tarot Suite, (1994) was inspired by a love of mythology and symbolism, which reflected the archetypal journey of human life through an interdisciplinary pan-continental approach.

Wallen’s study of cognitive psychology has aided his transition towards conceptualizing music as a medium for healing. Wallen raises awareness and invokes change by unlocking boundaries through the nature and science of sound.

Widely recognized as a seminal figure in Jazz, Wallen is an acclaimed writer and producer whose original scores have been commissioned by the Science Museum; PRS, The BBC, Jerwood Foundation, Southbank Centre, National Theatre, Arts Council, FIFA, and Sage Gateshead. He has also composed soundscapes for Universal Pictures, Warner Bros and Game of Thrones.

Wallen’s latest album "Portrait" featuring his band 4 corners is a homage to his adopted home in southeast London. The project forged new links between schools, venues, musicians, and residents to strengthen resilience and promote the cohesion of the community.

Wallen has received the BBC Jazz Innovation award (2003) and has been nominated several times for the MOBO award. In 2017 he received the coveted Paul Hamlyn Award. In 2020 his band Four Corners was nominated for the best band category at the Parliamentary Jazz Awards and best album in 2021.