The charity said Calum has accepted a new role as CEO of a Birmingham-based organisation and will leave on 19 August.
Calum said: “Leading Team KPG has been one of the highlights of my career and I am immensely proud of how the team have developed.
“They are an amazing group of people with an enormous amount of talent, passion and resilience, and I have complete confidence in what they will continue to accomplish moving forward, supported by an exceptional Board who remain fully committed to securing a bright future for the charity.”
The charity said that Calum had brought “greater commercial rigour” to its structure and is in “a stronger position as a result of his leadership”.
Dave Rogers,chair of the board of trustees, said: "Calum has made a real and lasting contribution to The Kaleidoscope Plus Group.
“I speak for the whole Board in thanking him for his continued focus and support during his notice period and wish him well in his new role.
“We are proud of what has been achieved during his time here and we go into this next chapter with strong foundations and an empowered, confident team.”
