Klum has worked full-time as a freelance photographer since 1986, and as a cinematographer and director on numerous film and television projects since 1994.
Klum describes and portrays animals, plants, and natural and cultural settings in the form of articles, books, films, lectures and exhibitions.
Klum has had several wildlife documentaries shown on Swedish national TV and has also had his work featured in Wildlife Conservation, Audubon, Geo, National Geographic, Terre sauvage, Stern, Der Spiegel and the New York Times among others.
In 1997 National Geographic Magazine published Mattias Klum's photographs for the first time, which made him the first Swede to have his work on the cover, then he was one of National Geographic's youngest contributors.
Since 1997, he has produced a number of articles and twelve cover stories for the magazine, including "Malaysia's Secret Realm" (August 1997), "Asia's Last Lions" (June 2001), "Meerkats Stand Tall" (September 2002), "What Darwin Didn't Know" (February 2009) and "The Bite That Heals" (February 2013).
Klum's photographs have been exhibited in one-man shows at reputable museums and art galleries in the US, Sweden, Malaysia, India, Japan, Great Britain, Estonia, Denmark, Botswana, Spain, China and Singapore among other countries.
He has also coached and collaborated with Sweden's Prince Carl Philip.
The book, The Human Quest: Prospering Within Planetary Boundaries, is co-authored by scientist and global sustainability expert Johan Rockström with a foreword by former President Bill Clinton.Mattias Klum's latest book ”Världar av Liv” was published in 2013 by Max Ström.
In 2013 Klum has also been awarded an Honorary Doctorate degree in Natural Science by Stockholm University and named WWF, the World Wildlife Fund ambassador.