[1] It has a membership that is primarily based in the UK,[2] but with additional members from outside Britain.

The 100 Marathon Club is affiliated to UK Athletics.

The 100 Marathon Club has two types of membership: full and associate.

Full membership is available to anyone who has run and completed at least 100 marathons or Ultra Marathons (ultras), whereas for associate membership, a runner only needs to have run at least 50 marathons or Ultras.

There are other 100 Marathon Clubs outside the UK, unconnected with the British one, including: