All 40,000 runners taking part in the annual race were given Heads Together headbands to raise awareness about mental health, and many of them are raising money for the campaign.
Kate Middleton wore a black Heads Together jacket with black skinny jeans and sneakers.
The London Marathon begins at points in Greenwich Park, St. John’s Park and Shooter’s Hill. The route continues east then heads towards the City with Tower Bridge as the half-way mark. The runners will pass through Embankment then will complete the course at The Mall by Buckingham Palace.
The event is divided into categories with groups such as wheelchair participants, elite women and elite men, all with different start times. The mini-marathon, a three-mile race for young runners, begins first.
The royal trio has been working hard to support the campaign. Last week the duke and duchess joined Prince Harry to launch a school called the Global Academy in West London. They headed to the school in Hayes, London, met with students and took part in a Heart radio breakfast show, broadcast from the Global Academy. The talk was held with students — and Spice Girl Emma Bunton — and focused on topics pertaining to mental health.
The duchess also stepped out and met with runners who are supporting the Heads Together campaign. She also helped to launch Royal Mail mailboxes decorated with light blue Heads Together headbands, which are situated along the London Marathon route.