London Marathon Events confirmed on Friday, June 19, 2026, that the 2027 London Marathon will expand into a historic two-day event on Saturday, April 24, and Sunday, April 25, 2027.
The unprecedented move, called "the Double," will allow a record-breaking 100,000 participants to run the iconic course from Greenwich to Westminster.
This nearly doubles the 60,512 runners who started the 2026 race.
Organizers designed the one-off format change to manage overwhelming demand, following a record 1.33 million applicants in the ballot for the upcoming event.
New Structure for Elite and Mass Participation
Under the new structure, elite women, elite female para-athletes, championship, and "good for age" women will compete on one day alongside a mixed mass participation field of nearly 50,000 runners.
The alternate day will feature elite men, elite male para-athletes, championship, and "good for age" men headlining a second mass participation event.
Participants cannot run on both days.
To support local communities, every London borough along the route will receive extra guaranteed entries, and every London school will receive two guaranteed places for staff members.
The expansion is projected to generate a £400 million social and economic benefit for the UK economy and smash fundraising records, following a 2026 event that has raised more than £90 million so far.
The plan secured critical backing from the London mayor's office after initial institutional resistance, as Transport for London voiced concerns about closing the capital across two consecutive days.
Hugh Brasher, CEO of London Marathon Events, said: "The 2027 TCS London Marathon Double is our most ambitious evolution to date – a once-in-a-generation one-time-only reimagining of what a marathon and city-wide celebration of activity can be."
He highlighted that the expanded field aims to maximize the event's social and financial impact across the United Kingdom.
"By expanding to 100,000 runners across two days, we’re opening the door for more people, more charities and more communities to take part in the world’s greatest marathon," Brasher added.
Mayor of London Sadiq Khan endorsed the expansion, stating: "London is the sporting capital of the world and I am delighted that, for one year only in 2027, the world famous TCS London Marathon will expand into a two-day event."
Khan emphasized the philanthropic scale: "This unique, one-off double will allow a record 100,000 participants to take part across the two days – creating the largest fundraising moment in UK sporting history."
City management teams are coordinating logistical operations to accommodate the expanded infrastructure requirements. Ballot applicants will receive official notifications in early July.
