The 100-year-old won the TV presenter prize, being nominated alongside Alison Hammond, Ant and Dec, Claudia Winkleman and Stacey Solomon.
Sir David did not attend the ceremony and his speech was read out on his behalf.
"I hope this award is a response to the part television has played in growing recognition, not only for the terrible plight our wonderful planet is in as a result of human activity but also of the fact we now have a pressing responsibility to do what we can to protect and conserve it," he wrote.
"I am honoured indeed. We are increasingly aware that if we are to repair the planet we need major national and international initiatives which certainly require our support, but it is also possible to make small differences in our own spaces and neighbourhoods.
"If enough small differences are made they do add up to doing something significant, while also providing spaces that we do enjoy being in and nurturing.
"Humanity has always needed the natural world for all the practicalities of life and for our mental wellbeing. Now the natural world needs us too. Surely we must not ignore that simple fact."
Sir David began his presenting career hosting Zoo Quest in 1954, going on to front documentary series The Life Collection, Natural World, Wildlife on One, the Planet Earth franchise, The Blue Planet and Frozen Planet.
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