Tom Clark has been with Scarborough RNLI for more than 30 years and was made Coxswain in 2002.
He was awarded an MBE in 2016 for his service to the RNLI and the Scarborough Sub-Aqua Club.
An RNLI spokesperson confirmed he had now left his role.
They said: "An internal RNLI investigation has recently been concluded into an incident at Scarborough lifeboat station and, as a result, the volunteer coxswain involved has been permanently stood down.
"Both the inshore and all weather lifeboats at Scarborough remain on service. The volunteer crew continue to work closely with the RNLI and the lifesaving operation has not been impacted by this decision.
"The RNLI was made aware of an unauthorised all weather lifeboat training exercise led by the coxswain. It is not acceptable to take out the lifeboat under these circumstances, without proper permissions, and subsequent evidence during the investigation contributed to the decision to stand him down.
"As an emergency service, the RNLI expects its crew members to behave professionally - not just in terms of maritime expertise, but also in behaviour and respect for others - and to carry out their role with due care and diligence at all times."