Cook provided guitar, vocals, and songwriting in the group, and remained involved with its creative and production aspects after his retirement.

He also remains active in many music projects, including, writing and performing with the Sydney soul-rock band The Soul Movers.

[7] When the Wiggles received honorary degrees from the Australian Catholic University in 2006, Cook gave the commencement speech to the graduates.

[9] Cook told the Newcastle Herald, about his music career after his retirement from the Wiggles, "I was kind of feeling my way for a few years, I guess".

Also in 2015, Cook was involved in the production of the play Sons of Sun, which was about American music producer Sam Phillips.

[11] In October 2017, Cook played guitar for the tribute show "The Nancy Sinatra/Lee Hazlewood Experience" with Zoe Carides and Scott Holmes in Newcastle, New South Wales.

[13] In 2015, Cook began writing songs with Mack and decided to focus on the band and use it as his "main creative outlet"[10] In 2017, the group recorded Testify, "an album of energetic blues, soul and rock".