For ITIL Foundation, there is exists no mandatory prerequisites
For ITIL Intermediate Service Lifecycle module certifications, the eligibility criteria are as follows:
You have to hold 2 credits from the ITIL Foundation certification examination.
You must hold 21 contact hours of instruction for the syllabus with an accredited training organization.
Two years of work experience in ITSM is recommended.
For all the Service Capability module certifications, you need to satisfy the following eligibility requirements:
You have to gain 2 credits from the ITIL Foundation certification examination.
You need  30 contact hours of instruction for the syllabus with an accredited training organization.
Two years of work experience in ITSM is recommended.
For ITIL Practitioner, an individual needs either an ITIL v3 Foundation or an ITIL 4 Foundation certificate. ITIL Practitioner is not a prerequisite for the ITIL Intermediate Level certifications.