A goalkeeper during his playing days, Larrieu joined Argyle in 2000 and made more than 300 appearances despite enduring a successful battle against testicular cancer.
Boss John Sheridan has also moved first-team coach Kevin Nancekivell down to youth-team duties and thanked both men for their contributions.
He told Plymouth's official website: ""I would like to thank Romain and Kevin for the support that they have given me since I have been at the club.
"I could not have asked for more. But it is my job as a manager to make the decisions that I think are going to push the club forward."