RIA Member – London 100

London 100 is central London’s only ultramarathon.

London 100 includes three challenge distances: 100km, 50km, and 25km, making the event suitable for experienced ultramarathoners, as well as for those looking to step up from marathons or half marathons. Following a successful inaugural event this year, London’s longest run returns to the streets of the capital on Saturday 9 May 2026.

Starting from a superb and spacious indoor Central London Run HQ, four unique 25km routes explore the north, south, east, and west of the capital in a ‘clover leaf’ formation. Participants experience areas of London they never knew existed, discover hidden trails, and pass 100 famous sights and landmarks of one of the world’s greatest cities, all in one long run.

London 100 (2025) saw participants from all over the world. Entrants included a running club in France and several runners from New York City (a city that also hosts its own 100km urban-ultra). The event was supported by some of the best running communities in London, something which added a unique and uplifting experience for all. London 100 has great access to hotels and restaurants, and an abundance of travel options making it accessible and the perfect event for groups of runners looking for a different and memorable experience.

Our spacious central London Run HQ allows us to showcase some of the best running brands. Several of these brands including Stolt Running, SUMs and Precision Fuel & Hydration joined us for the full day to proudly showcase their products. The event is also supported by several London 100 Route Recce Runs with brand partners taking an ownership for each – a brilliant way for runners to get to know each other, learn some of the nuances of the course and to meet the brands in an informal way.

Website: www.london100km.com

Follow on Instagram: www.instagram.com/london100km