The London Marathon will expand to a two-day format in 2027, with races scheduled for Saturday 24 and Sunday 25 April. This special one-off edition responds to unprecedented demand, as a record 1.33 million applicants entered the ballot for next year's event. The dual-day structure will accommodate 100,000 runners, effectively doubling participation opportunities for hopefuls.

Organisers project the expanded event will generate over £150m for charities and deliver a £400m boost to the UK economy. Hugh Brasher, chief executive of London Marathon Events, called it the organization's 'most ambitious evolution to date' and emphasized the social and economic benefits. The initiative has been nine years in development, initially conceived in 2017 but delayed due to permission issues.

All 100,000 participants will follow the traditional Greenwich to Westminster route. Elite women and female wheelchair athletes will lead Saturday's mass event, while elite men and male wheelchair competitors headline Sunday. The Saturday ballot draw will follow the Sunday selection, ensuring fair allocation across both days. Additionally, the Mini London Marathon takes place on Friday with over 20,000 young participants.

Brasher confirmed this represents a one-time-only reimagining of the world's greatest marathon, with additional income directed toward youth activity projects through the London Marathon Foundation. Mayor Sadiq Khan endorsed the move, calling London the 'sporting capital of the world.'