The former communications head at Conservative Party headquarters was attending a bird-watching conference, Birdfair, at Rutland Nature Reserve.
It is her first solo outing since Boris Johnson took office in July.
But the eco-conscious “first girlfriend” used her speech to take aim at ‘trophy hunters’ and those who take part in illegal sports that target animals.
She arrived wearing an ‘eco friendly’ dress that reportedly cost £225 and green wellington boots, with a red handbag as she arrived on Friday afternoon.
She told crowds during her State of The Earth Question Time appearance: “Why would anyone want to destroy something so beautiful, then stuff its poor lifeless body to keep as some kind of macabre trophy?
“A trophy is meant to be a prize, something you’re awarded if you’ve achieved something of merit that requires great skill and talent.
“Trophy hunting is not that - it is the opposite of that.
“It is cruel, it is sick, it is cowardly and I will never, ever understand the motivation to do it.”
Following her speech, she will sit on a panel style show, alongside experts such as BBC Springwatch presenter Chris Packham.
After resigning from Tory HQ, the UK’s ‘first girlfriend’ is now a marketing senior adviser at Oceana, a US-based environmental campaign group.
Ms Symonds was first seen in the public eye following reports of police responding to her and Mr Johnson’s home during the Tory leadership race.
Birdfair attracts over 240,000 people mo its three day event.
Birdfair founder Tim Appleton said: “We’re absolutely over the moon that Carrie is supporting us and we hope she will continue supporting us and conservation for many years to come.”