Princess Beatrice and her American boyfriend David Clark were a part of the 'human caterpillar" consisting of 34 people.
The participants were tied together with bungee cords for the 26.2 mile long race. Princess Beatrice participated in the marathon for raising charity for Children in Crisis.
The princess wore a lime green tutu over her running gear. Her parents at the finishing line congratulated her.
Other celebrity runners included Sir Richard Branson, TV presenter Lorraine Kelly and singer Natalie Imbruglia.