2021 British Athletics Marathon and 20 km Walk Trial

The 2021 British Athletics Marathon and 20 km Walk Trial (known for sponsorship reasons as the Müller British Athletics Marathon and 20 km Walk Trials) was held on 26 March 2021 as a trial event for British athletes to qualify for the delayed 2020 Summer Olympics in Tokyo. It was the first time since 1980 that a dedicated marathon trial event was held, and the courses consisted of multiple laps around Kew Gardens in London.

The marathon events were won by Chris Thompson and Stephanie Davis, both of whom qualified for the Olympics as a result. The 20 km walk events were won by Callum Wilkinson and Heather Lewis, both of whom finished outside their respective Olympic qualifying times; Wilkinson was later awarded a place at the Olympics. Ben Connor and Tom Bosworth also qualified for the marathon and 20 km walk Olympic events respectively due to their finishing positions.