The attraction won the title at the 2012 Group Travel Awards held at the Park Plaza Riverbank Hotel in London.
Longleat beat off challenges from Chester Zoo, London Aquarium, Whipsnade Zoo and Woburn Safari Park to claim the top prize, which was presented by travel journalist Simon Calder.
Longleat’s Florence Wallace said: “We’re absolutely delighted to have won this award; particularly as we were up against such strong opposition.
“The award is voted for by people working in the travel trade industry which makes it especially rewarding for us to have been recognised by our peers.
“Over the past 18 months Longleat has embarked on a major and ongoing programme of investment and acquisition to cement our position as the number one Safari and Adventure Park in the UK.
“In addition to acquiring The Bishopstrow House and Spa Hotel in Warminster and Homewood Park Hotel & Spa in Hinton Charterhouse we have invested in a series of major new features and events at Longleat.
“These include Cheetah Kingdom, a new giraffe feeding platform, a major new lakeside gorilla enclosure and a walkthrough lemur exhibit as well as major new events for Easter, Halloween and Christmas.
“We have also put together exciting new initiatives aimed specifically at the groups market including tailor-made tours as well as setting up a dedicated sales team and this award is an indication that we are moving in the right direction,” she added.
The Group Travel Awards are voted on by readers of Group Travel Organiser magazine.