The initial contract runs from now until July 2017, with Black Diamond tasked with positioning the State of Colorado as an adventurous destination.
The agency will focus on the 'Come to Life' campaign strategy and create partnerships aiming to attract attention to Colorado’s festivals and events.
Black Diamond will be working alongside Colorado Tourism Office’s Denver-based advertising agency, Karsh Hagan.
"The UK and Ireland represent the largest overseas travel market to the United States, with more than two million travellers from these countries visiting the US last year," said Cathy Ritter, director of Colorado Tourism Office.
"We look forward to working with Black Diamond and creating innovations and partnerships to help us market the State of Colorado and to provide travellers from the UK and Ireland with an extraordinary travel experience."
London's Black Diamond also works with clients including Visit California, OWL Watches, San Francisco Travel Association and South African Airways.